733. Describe the appearance of the brain when a horizontal section has been made. What is the gray border often called? What connects the hemispheres? 734. Describe the ventricles of the brain. In the disease called "dropsy of the brain," where is the water deposited? 735. What is the character of the brain in childhood? In adults? 736. How does the cerebellum compare in size with the cerebrum?
[Illustration: Fig. 122. The under surface, or base, of the brain and origin of the cranial nerves. 1, 1, The anterior lobes of the cerebrum. 2, 2, The middle lobes. 3, 3, The posterior lobes, almost concealed by the cerebellum. 4, 4, The cerebellum. 7, 7, The longitudinal fissure that divides the brain into two hemispheres. 8, The first pair of nerves. 9, 9, The second pair of nerves. 10, The decussation, or crossing, of its fibres. 13, 13, The third pair of nerves. 14, The pons varolii. 15, 15, The fourth pair of nerves. 16, 16, The fifth pair of nerves. 17, The sixth pair of nerves. 18, 18, The seventh and eighth pair of nerves. 19, The medulla oblongata, with the crossing of some of its fibres exhibited. 20, The ninth pair of nerves. 21, The tenth pair of nerves, 22, The eleventh pair of nerves. 23, The twelfth pair of nerves.]
Describe this portion of the brain. Explain fig. 122.
737. The MEDULLA OBLONGATA, or that portion of the spinal cord which is within the skull, consists of three pairs of bodies, (cor'pus py-ram-i-da'le, res-ti-for'me, and ol-i-va're,) united in a single bulb.
[Illustration: Fig. 123. The base of the skull and the openings through which the cranial nerves pass. 1, 1, The first pair of nerves. 2, 2, The cribriform plate of the ethmoid bone through which this nerve passes. 3, 3, The second pair of nerves. 4, 4, The optic foramen in the sphenoid bone; through which passes the second pair of nerves. 5, 5, The sphenoidal fissure. 6, 6, The third pair of nerves. 7, 7, The fifth pair of nerves. 8, 8, The ophthalmic branch of the fifth nerve. The third, the ophthalmic branch of the fifth and the sixth nerve pass from the brain through the sphenoidal fissure to the eye. 9, 9, The superior maxillary branch of the fifth nerve. 10, 10, The foramen rotundum, (round opening,) through which the nerve 9, 9, passes to the upper jaw. 11, 11, The inferior maxillary branch of the fifth pair. 12, 12, The foramen ovale, (oval opening,) through which the nerve 11, 11, passes to the lower jaw. 13, 13, The sixth pair of nerves. 14, 14, The seventh and eighth pair of nerves. 15, 15, The opening in the temporal bone, through which the seventh and eighth nerves pass to the face and ear. 16, 16, The ninth pair of nerves. 17, The tenth pair of nerves. 18, 18, The eleventh pair of nerves. 19, 19, The foramen lacerum (rough opening.) The ninth, tenth, and eleventh nerves pass from the brain through this opening. 20, The spinal cord. 21, The foramen spinalis, through which the spinal cord passes. 22, 22, The position of the anterior lobe of the brain. 23, 23, The middle lobe. 24, 24, The posterior lobe. 25, 25, A section of the skull-bones.]
737. Describe the medulla oblongata. Explain fig. 123.
738. The DURA MATER is a firm, fibrous membrane, which is exposed on the removal of a section of the skull-bones. This lines the interior of the skull and spinal column, and likewise sends processes inward, for the support and protection of the different parts of the brain. It also sends processes externally, which form the sheaths for the nerves, as they quit the skull and spinal column. The dura mater is supplied with arteries and nerves.
738. Describe the dura mater. What is its use? Explain fig. 124.
739. The ARACHNOID, so called from its extreme tenuity, is the serous membrane of the brain and spinal cord, and is, like other serous membranes, a closed sac. It envelops these organs, and is reflected upon the inner surface of the dura mater, giving to that membrane its serous investment.
740. The PIA MATER is a vascular membrane, composed of innumerable vessels, held together by cellular membrane. It invests the whole surface of the brain, and dips into its convolutions. The pia mater is the nutrient membrane of the brain, and receives its blood from the carotid and vertebral arteries. Its nerves are minute branches of the sympathetic, which accompany the branches of the arteries.
741. The CRANIAL NERVES, that connect with the brain, are arranged in twelve pairs. They are called: 1st. The Ol-fact'o-ry. 2d. The Op'tic. 3d. The Mo-to'res Oc-u-lo'rum. 4th. The Pa-thet'i-cus. 5th. The Tri-fa'cial. 6th. The Ab-du-cen'tes. 7th. The Por'ti-o Du'ra. 8th. The Por'ti-o Mol'lis. 9th. The Glos'so-pha-ryn'gi-al. 10th. The Pneu-mo-gas'tric. 11th. The Spi'nal Ac'ces-so-ry. 12th. The Hy'po-glos'sal.
742. The OLFACTORY NERVE (first pair) passes from the cavity of the skull through many small openings in a plate of the eth'moid bone. (This plate is called crib'ri-form, from its resemblance to a sieve.) This nerve ramifies upon the membrane that lines the nasal passages. It is the softest nerve of the body. (Fig. 136.)
743. The OPTIC NERVE (second pair) passes from the interior of the cranium, through an opening in the base of the skull, (fo-ra'men op'ti-cum,) to the cavity for the eye. It pierces the coats of the eye, and expands in the retina.
744. The MOTORES OCULORUM (third pair) pass from the brain, through an opening of the sphe'noid bone, (sphe-noid'al fis'sure,) to the muscles of the eye.
739. Describe the arachnoid membrane. 740. What is said respecting the pia mater? 741. How many pairs of cranial nerves? Name them. 742. Describe the olfactory nerve. 743. The optic nerve. 744. Describe the motores oculorum.
745. The PATHETICUS (fourth pair) passes from the brain, through the sphenoidal fissure, to the superior oblique muscle of the eye.
746. The TRIFACIAL NERVE (fifth pair) is analogous to the spinal nerves in its origin by two roots, from the anterior and posterior columns of the spinal cord. It has a ganglion, like the spinal nerves upon its posterior root. For these reasons, it ranges with the spinal nerves, and is considered the cranial spinal nerve. This nerve divides into three branches:—The oph-thal'mic, superior max'il-la-ry, and inferior max'il-la-ry.
745. The patheticus. What does fig. 125 represent? 746. What is the trifacial nerve sometimes called? Why is it classed with the cranial spinal nerves? Give the names of its branches.
747. The ophthalmic nerve passes from the cranial cavity through the sphenoidal fissure. It sends branches to the forehead, eye, and nose. The superior maxillary nerve passes through an opening in the base of the skull, (foramen ro-tund'dum,) and sends branches to the eye, the teeth of the upper jaw, and the muscles of the face. The inferior maxillary nerve escapes from the cranial cavity through an opening called foramen o-va'le. It sends branches to the muscles of the lower jaw, the ear, the tongue, and the teeth of the lower jaw.
747. Where do the filaments of the ophthalmic branch ramify? The superior maxillary? The inferior maxillary? Explain fig. 126.
748. The ABDUCENTES (sixth pair) passes through the opening by which the carotid artery enters the cranial cavity. It is the smallest of the cerebral nerves, and is appropriated to the external straight muscle of the eye.
749. The PORTIO MOLLIS (seventh pair) enters the hard portion of the tem'po-ral bone at the internal auditory opening, and is distributed upon the internal ear. (Fig. 147, 148.)
750. The FACIAL NERVE (eighth pair) passes from the skull through an opening situated below the ear, (mas'toid foramen.) It is distributed over the face, supplying the muscles with nervous filaments.
748. What is said of the abducentes, or sixth pair of nerves? 749. Of the portio mollis? Explain fig. 127. 750. Of the facial nerve?
751. The GLOSSO-PHARYNGEAL NERVE (ninth pair) passes from the brain, through an opening with the jugular vein, (foramen lac'e-rum.) It is distributed to the mucous membrane of the tongue and throat, and also to the mucous glands of the mouth.
752. the PNEUMOGASTRIC NERVE (tenth pair) escapes from the brain through the foramen lacerum. It sends branches to the larynx, pharynx, oesophagus, lungs, spleen, pancreas, liver, stomach, and intestines. (Fig. 132.)
753. The SPINAL ACCESSORY NERVE (eleventh pair) has its origin in the respiratory tract of the spinal cord. It connects with the ninth and tenth pairs of nerves, and is distributed to the muscles about the neck.
754. The HYPO-GLOSSAL NERVE (twelfth pair) passes from the brain, through a small opening, (con'dy-loid foramen.) It ramifies upon the muscles of the tongue, and is its motor nerve.
Observation. The cranial nerves, with the exception of the olfactory, optic, and auditory, connect with each other by means of filaments. They also send connecting nervous filaments to the upper spinal nerves, (cervical,) and the sympathetic nerve.
751. Describe the glosso-pharyngeal nerve. 752. The pneumogastric nerve. 753. The spinal accessory nerve. 754. The hypo-glossal nerve.
ANATOMY OF THE NERVOUS SYSTEM, CONTINUED.
755. The spinal column contains the spinal cord, the roots of the spinal nerves, and the membranes of the cord.
756. The SPINAL CORD extends from the medulla oblongata to the second lumbar vertebra, where it terminates in a rounded point. It presents a difference of diameter in different parts of its extent, and exhibits three enlargements. The uppermost of these is the medulla oblongata. There is no distinct demarkation between this enlargement and the spinal cord. The next corresponds with the origin of the nerves distributed to the upper extremities; the third enlargement is situated near the termination of the cord, and corresponds with the attachment of the nerves which are intended for the supply of the lower extremities.
757. An anterior and posterior fissure divides the spinal cord into two lateral cords. These are united by a thin layer of white substance. The lateral cords are each divided by furrows into three distinct sets of fibres, or columns; namely the anterior, lateral, and posterior columns. The anterior are the motor columns; the posterior are the columns of sensation; the lateral columns are divided in their function between motion and sensation. They contain the fasciculus described, by Sir Charles Bell, as the respiratory tract.
755-767. Give the anatomy of the spinal cord, spinal nerves, and the sympathetic nerve. 755. What does the spinal column contain? 756. Give the extent of the spinal cord. How many enlargements has this cord? What is said of each enlargement? 757. Into how many parts is the spinal cord divided? Give the function of these columns.
758. The SPINAL NERVES, that connect with the spinal cord, are arranged in thirty-one pairs, each arising by two roots; an anterior, or motor root, and a posterior, or sensitive root. Each nerve, when minutely examined, is found to consist of an aggregate of very delicate filaments, enclosed in a common cellular envelope.
758. How many pairs of nerves issue from the spinal cord? Explain fig. 128. Fig. 129.
759. The anterior roots arise from a narrow white line upon the anterior columns of the spinal cord. The posterior roots arise from a narrow gray band formed by the internal gray substance of the cord. They are larger, and the filaments of origin more numerous than those of the anterior roots. A ganglion is found upon each of the posterior roots in the openings between the bones of the spinal column through which the nerve passes.
760. After the formation of the ganglion, the two roots unite, and constitute a spinal nerve, which passes through the opening between the vertebrae on the sides of the spinal column. The nerves divide and subdivide, until their minute filaments ramify on the tissues of the different organs.
759. Give the origin of the anterior roots. Of the posterior roots. In what respect do the posterior roots differ from the anterior? 760. When do the two roots unite, and where do they pass?
761. The spinal nerves are divided into—
Cervical, 8 pairs, Dorsal, 12 " Lumbar, 5 " Sacral, 6 "
762. The four lower cervical and upper dorsal pass into each other and then separate to reunite. This is called the brach'i-al plex'us. From this plexus six nerves proceed, which ramify upon the muscles and skin of the upper extremities.
763. The last dorsal and the five lumbar nerves form a plexus called the lumbar, similar to that of the cervical. Six nerves pass from this plexus, which ramify upon the muscles and skin of the lower extremities.
764. The last lumbar and the four upper sacral unite to form the sacral plexus. From this plexus five nerves proceed, that are distributed to the muscles and skin of the hip and lower extremities.
765. The SYMPATHETIC NERVE consists of a series of Gan'gli-a, or knots, extending each side of the spinal column, forming a chain its whole length. It communicates with both the cranial and spinal nerves. With the exception of the neck, there is a ganglion for each intervertebral space. These ganglia are composed of a mixture of cineritious and medullary matter, and are supposed to be productive of peculiar nervous power.
 The structure of this nerve is very complicated, and different physiologists ascribe to it various functions. The character of its diseases are not well understood.
761. Give the division of the spinal nerves. 762. What nerves constitute the brachial plexus? How many nerves pass from this plexus? 763. How many nerves from the lumbar plexus, and where do they ramify? 764. How is the sacral plexus formed? 765. Of what does the sympathetic nerve consist? How is the sympathetic nerve distributed? What exception? Of what are the ganglia composed?
[Illustration: Fig. 131. A beautiful representation of the sympathetic ganglia and their connection with other nerves. It is from the grand engraving of Manec, reduced in size. A, A, A, The semilunar ganglion and solar plexus, situated below the diaphragm and behind the stomach. This ganglion is situated in the region (pit of the stomach) where a blow gives severe suffering. D, D, D, The thoracic ganglia, ten or eleven in number. E, E, The external and internal branches of the thoracic ganglia. G, H, The right and left coronary plexus, situated upon the heart. I, N, Q, The inferior, middle, and superior cervical ganglia. 1, The renal plexus of nerves that surrounds the kidneys. 2, The lumbar ganglion. 3, Their internal branches. 4, Their external branches. 5, The aortic plexus of nerves that lies upon the aorta. The other letters and figures represent nerves that connect important organs and nerves with the sympathetic ganglia.]
766. The GANGLIA may be considered as distinct centres, giving off branches in four directions; namely, the superior, or ascending, to communicate with the ganglion above; the inferior, or descending, to communicate with the ganglion below; the external, to communicate with the spinal nerves; and the internal, to communicate with the sympathetic filaments. It is generally admitted that the nerves that pass from the ganglia are larger than those that entered them; as if they imparted to the nerve some additional power.
767. The branches of distribution accompany the arteries which supply the different organs, and form communications around them, which are called plexuses, and take the name of the artery with which they are associated. Thus we have the mesenteric plexus, hepatic plexus, splenic plexus, &c. All the internal organs of the head, neck, and trunk, are supplied with branches from the sympathetic, and some of them exclusively; for this reason, it is considered a nerve of organic life.
What is the design of fig, 131? 766. How may the ganglia be considered? 767. What is said of the branches of the sympathetic nerve?
PHYSIOLOGY OF THE NERVOUS SYSTEM.
768. The brain is regarded by physiologists and philosophers as the organ of the mind. Most writers consider it as an aggregate of parts, each charged with specific functions, and that these functions are the highest and most important in the animal economy. To the large brain, or cerebral lobes, they ascribe the seat of the faculties of thinking, memory, and the will. In man, this lobe extends so far backward as to cover the whole of the cerebellum. To the cerebellum, or little brain, is ascribed the seat of the animal, or lower propensities.
769. "The constant relation between mental power and development of brain, explains why capacities and dispositions are so different. In infancy, for example, the intellectual powers are feeble and inactive. This arises partly from the inaptitude of a still imperfect brain; but in proportion as the latter advances toward its mature state, the mental faculties also become vigorous and active."
770. We are able, in most instances, at least, to trace a correspondence between the development of the cerebral lobes and the amount of intelligence possessed by the person. The weight of the brain in man to that of the whole body varies in different individuals. The heaviest brain on record was that of Cuvier, which weighed 4 pounds and 13 1/2 ounces.
768-772. Give the physiology of the nervous system. 768. How is the brain regarded by physiologists and philosophers? What do they ascribe to the cerebrum? To the cerebellum? 769. What does the relation between mental powers and development of brain explain? 770. What is said respecting the correspondence between the development of the brain and the amount of intelligence possessed by the person? What is said of the weight of the brain?
771. The brain likewise holds an important relation to all the other organs of the system. To the muscular system it imparts an influence which induces contraction of the fibres. By this relation they are brought under the control of the will. To the skin, eye, and ear, it imparts an influence that gives sensibility, or the power of feeling, seeing, hearing, &c.
772. Again, the involuntary functions of the different portions of the system are more or less influenced by the brain. If the action of this central organ of the nervous system is destroyed, the functions of the digestive, respiratory, and circulatory apparatuses will be much disturbed or entirely suppressed.
773. The brain is the seat of sensation. It receives the impressions made on all parts of the body, through the medium of the sensitive nerves. That the impressions of external objects, made on these nerves, be communicated to the brain, where sensation is perceived, it is necessary that they be not diseased or injured.
Observation. There is a plain distinction between sensations and impressions; the latter are the changes produced in the extremities of the nerve; the former, the changes produced in the brain and communicated to the mind.
774. What part of the brain receives the impressions or has the most intimate relation with the intellectual faculties is unknown. Some portions, however, are of less importance than others. Large portions of the cortical, or outer part, are frequently removed without affecting the functions of this organ. Pieces of the medullary, or central parts, have been removed by injuries without impairing the intellect or destroying life. This organ, although it takes cognizance of every sensation, is, of itself, but slightly sensible. It may be cut, or parts may be removed without pain, and the individual, at the same times retain his consciousness.
771. What is said of the relation of the brain to all of the organs of the body? 772. Are the involuntary functions of different parts of the system influenced by the brain? 773. Where is sensation perceived? By what agency are the impressions of external objects conveyed to the brain? What is the difference between sensations and impressions? 774. Is it known what part of the brain has the most intimate relation with the intellectual faculties?
775. The brain is the seat of the will. It superintends the physical as well as the mental movements, and the medium of communication from this organ to the muscles, or the parts to be moved, is the motor nerves. If the brain is in a quiescent state, the muscles are at rest; if, by an act of the will, the brain sends a portion of nervous influence to a voluntary muscle, it immediately contracts, and those parts to which the muscle is attached move. There is no perceptible interval between the act of the will and the motion of the part.
776. Some physiologists assert, that the medulla oblongata is the point at which excitement to motion commences, and sensation terminates; and also, that it possesses the power of originating motion in itself.
Observation. The medulla oblongata, unlike the brain, is highly sensitive; if slightly punctured, convulsions follow; if much injured, respiration, or breathing, immediately ceases.
777. It is remarkable that the nerves which arise from the right side of the spinal cord communicate with the left hemisphere of the cerebrum, and vice versa; this results from the crossing of the fibres in the medulla oblongata. It follows from this, that if the right side of the brain receives an injury, the parts of the opposite side of the body lose their sensibility and motion.
Observations. 1st. If the cranial nerves which are connected by a single root are divided, only the sensation of the part to which they are distributed is lost. Thus, if the optic nerve is divided, the sense of vision disappears, but the motions of the eye are performed as readily as before. But, if the spinal nerves are divided, both sensation and motion of the part to which they lead are destroyed.
What portions have been removed without impairing the intellect? What is remarkable of the brain? 775. What is the influence of the brain upon the muscles? 776. What do some physiologists assert of the medulla oblongata? 777. What is remarkable of the nerves? Give the 1st observation relative to the cranial nerves.
2d. When the spinal cord is divided or compressed, as in fractures of the spinal column, all parts below the fracture are paralyzed, though the nerves leading to these parts may be uninjured.
3d. Again, one side of the body or one limb may become insensible, and the power to move it, be perfectly retained; or the reverse of this may happen—the power of motion will be lost while sensation remains. In the former instance, the function of the posterior, or sensitive column of the spinal cord on one side is destroyed; in the latter, the anterior, or motor column is affected.
4th. In some cases, both sensation and motion of one side of the body or one limb are destroyed. In such instances, both the anterior and the posterior columns of one side of the spinal cord are diseased.
778. Vigorous and controllable muscular contraction requires a sound and well-developed brain. If this organ is defective in these particulars, the movements will be inefficient, and may be irregular. The central organ of the nervous system must, likewise, be in an active condition, to induce regular, steady, and controllable muscular movements.
Observations. 1st. Persons who have suffered from apoplexy and other severe diseases of the brain, have an involuntary trembling of the limbs, which results from a weakened state of the nervous system.
To the spinal nerves. What is said of the compression of the spinal cord? Give the 3d observation relative to the spinal nerves. The 4th observation. 778. Upon what does vigorous controllable muscular contraction depend? What causes the involuntary trembling of the limbs in persons who have suffered from apoplexy?
2d. The tremor of the hand, that lessens the usefulness or incapacitates the fine artist or skilful mechanic, in the prime of life, from pursuing their vocations, may be, and is often, induced by the influence of intoxicating drink, which debilitates and disorganizes the brain.
3d. The tottering step, trembling hand, and shaking head of the aged invalid, are the results of diminished nervous energy, so that steady muscular contraction, so essential to regular movements, cannot be maintained.
779. No difference can be discovered in the structure of the several kinds of nerves in any part of their course, and the functions they are designed to perform can only be known by ascertaining the place of their origin. The nerves may be functionally divided into five groups.
780. 1st. Nerves of special sensation. These are the first, second, eighth, and it may be one of the branches of the fifth pair of cranial nerves. The function of these nerves is particularly described in the chapters upon the senses of smell, vision, hearing, and taste.
781. 2d. Nerves of general sensation. These embrace the fifth pair of cranial nerves, and the thirty-one pairs of spinal nerves. In those parts that require sensation for their safety and the performance of their functions, there is an abundant supply of sensitive nervous filaments. The nerves of sensation are mostly distributed upon the skin. Few filaments ramify upon the mucous membranes and muscles.
Observations. 1st. The painful sensations experienced in the face, and in the teeth or jaws, (tic douloureux and toothache,) are induced by irritation and disease of a portion of the filaments of the fifth pair of cranial nerves.
The tremor of the hand among some mechanics in the prime of life? The tottering step of the aged invalid? 779. What is said relative to the structure of the nerves? How may they be divided? 780. Give the nerves of special sense. 781. Those of general sensation. Where are the nerves of sensation distributed? What causes tic douloureux?
2d. The unpleasant sensation sometimes experienced when we hear the grating of a file or saw, is produced by the connection of the nerve that passes across the drum of the ear with the fifth cranial nerve.
3d. When pressure is made on the trunk of a nerve, the sensibility of the part where the nerve ramifies is modified. This is illustrated, when pressure is made upon the large nerve of the lower extremity (sciatic) in sitting upon a hard bench. The foot is then said to be "asleep."
4th. When the trunk of a nerve is diseased or injured, the pain is experienced in the outer extremity of the nerve. A blow upon the elbow, which causes a peculiar sensation in the little finger and one side of the ring finger, affords a familiar illustration. This sensation is produced by injuring the ulnar nerve, which is distributed to the little finger.
782. 3d. Nerves of motion. These are the third, sixth, and twelfth pairs of cranial nerves, and the thirty-one pairs of spinal nerves. These nerves are distributed to the fibres of the five hundred muscles of the body. The functions of the muscular are different from those of the sensitive nerves. The former are provided for the purpose of motion, and not of feeling. Hence, muscles may be cut, and the pain will be slight, compared with the cutting of the skin. This may be called muscular pain. Weariness is a sensation recognized by one set of muscular nerves.
783. So uniformly is a separate instrument provided for every additional function, that there is strong reason to regard the muscular nerves, although running in one sheath, as in reality double, and performing distinct functions. Sir Charles Bell, in his work on the Nervous System, endeavors to show, that one set of nervous fibres conveys the mandate from the brain to the muscle, and excites the contraction; and that another set conveys, from the muscle to the brain, a peculiar sense of the state or degree of contraction of the muscle, by which we are enabled to judge of the amount of stimulus necessary to accomplish the end desired. This is obviously an indispensable piece of information to the mind in regulating the movements of the body.
How is the peculiar sensation accounted for when we hear the grating of a file or saw? What produces the sensation when the foot is said to be "asleep?" What is the effect when the ulnar nerve is injured by a blow? 782. Give the nerves of motion. What is said of the functions of the muscular nerves? 783. What does Sir Charles Bell endeavor to show?
784. 4th. Nerves of respiration. These are the fourth, seventh, ninth, tenth, and eleventh pair of cranial nerves, also the phrenic and the external respiratory nerve. All of these nerves have their origin in a distinct tract or column, called the lateral, in the upper part of the spinal cord. Hence it is sometimes named the respiratory column. These nerves are distributed to one of the muscles of the eye; to the muscles of the face; to the tongue, pharynx, oesophagus, stomach, heart, lungs, diaphragm, and some of the muscles of the neck and chest.
785. It is through the instrumentality of the accessory, phrenic, and external respiratory nerves, (10, 11, 12, 13, fig. 132,) that the muscles employed in respiration are brought into action without the necessity of the interference of the mind. Though to a certain extent they may be under the influence of the will, yet it is only in a secondary degree. No one can long suspend the movements of respiration; for in a short time, instinctive feeling issues its irresistible mandate, which neither requires the aid of erring wisdom, nor brooks the capricious interference of the will.
 Dr. Elliotson, and some other writers On physiology, have detailed cases of death from voluntary suspension of respiration. But these cases are not conclusive, as examinations were not made, so as to determine positively, that death did not result from disease of the heart, brain, or some other vital organ.
[Illustration: Fig. 132. The distribution of the respiratory nerves. a, Section of the brain and medulla oblongata. b, The lateral columns of the spinal cord. c, c, The respiratory tract of the spinal cord. d, The tongue. e, The larynx. f, The bronchia. g, The oesophagus. h, The stomach. i, The diaphragm. 1, The pneumogastric nerve. 2, The superior laryngeal nerve. 3, The recurrent laryngeal nerve. (These two ramify on the larynx.) 4, The pulmonary plexus of the tenth nerve. 5, The cardiac plexus of the tenth nerve. These two plexuses supply the heart and lungs with nervous filaments. 7, The origin of the fourth pair of nerves, that passes to the superior oblique muscle of the eye. 8, The origin of the facial nerve, that is spread out on the side of the face and nose. 9, The origin of the glosso-pharyngeal nerve, that passes to the tongue and pharynx. 10, The origin of the spinal accessory nerve. 11, This nerve penetrating the sterno-mastoideus muscle. 12, The origin of the internal respiratory or phrenic nerve, that is seen to ramify on the diaphragm. 13, The origin of the external respiratory nerve, that ramifies on the pectoral and scaleni muscles.]
784. Give the respiratory nerves. What is said in reference to the respiratory nerves? 785. Through the agency of what nerves are the respiratory muscles brought into action? Explain fig. 132.
786. The fourth, seventh, and tenth pairs of nerves, (7, 8, 9, fig. 132,) with the spinal accessory, phrenic, and external respiratory, are not only connected with the function of respiration, but contribute to the expression of the passions and emotions of the mind.
787. The influence of this order of nerves in the expression of the passions, is strikingly depicted in Sir Charles Bell's Treatise on the Nervous System. "In terror," he remarks, "we can readily conceive why a man stands with his eyes intently fixed on the object of his fears—the eyebrows elevated, and the eyeballs largely uncovered; or why, with hesitating and bewildered steps, his eyes are rapidly and wildly in search of something. In this way, we only perceive the intense application of his mind to the objects of his apprehension, and its direct influence on the outward organs."
Can respiration be suspended for any considerable length of time? 786. What nerves contribute to the expression of the passions and emotions of the mind? 787, 788. What does Sir Charles Bell say of the influence of this order of nerves in the expression of the passions?
788. "But when we observe him further, there is a spasm in his breast; he cannot breathe freely; the chest remains elevated, and his respiration is short and rapid. There is a gasping and convulsive motion of his lips, a tremor on his hollow cheeks, a gasping and catching of his throat; his heart knocks at his ribs, while yet there is no force in the circulation—the lips and cheeks being ashy pale."
789. "These nerves are the instruments of expression, from the smile upon the infant's cheek, to the last agony of life. It is when the strong man is subdued by this mysterious influence of soul on body, and when the passions may be truly said to tear the heart, that we have the most afflicting picture of human frailty, and the most unequivocal proof that it is the order of functions we have been considering, that is thus affected. In the first struggle of the infant to draw breath, in the man recovering from a state of suffocation, and in the agony of passion, when the breast labors from the influence at the heart, the same system of parts is affected, the same nerves, the same muscles, and the symptoms or character have a strict resemblance."
790. The seventh pair of nerves not only communicates the purposes of the will to the muscles of the face, but at the same time it calls them into action, under the influence of instinct and sympathy. On this subject a late writer remarks, "How expressive is the face of man! How clearly it announces the thoughts and sentiments of the mind! How well depicted are the passions on his countenance! tumultuous rage, abject fear, devoted love, envy, hatred, grief, and every other emotion, in all their shades and diversities, are imprinted there, in characters so clear that he that runs may read! How difficult, nay, how impossible, is it to hide or falsify the expressions which indicate the internal feelings! Thus conscious guilt shrinks from detection, innocence declares its confidence, and hope anticipates with bright expectation."
Observation. The fifth pair of nerves (fig. 126) is distributed to the parts of the face on which the seventh pair ramifies. The former serves for sensation, the latter for motion. Thus, when the seventh pair of nerves is divided, or its functions destroyed by disease, the side affected loses all power of expression, though sensation remains unaffected. On the contrary, if we divide the fifth pair, sensation is entirely destroyed, while expression remains.
789. Are they also the instruments of expression, either of joy or grief? 790. What is said in reference to the seventh pair of nerves? Where is the fifth pair of nerves distributed?
791. 5th. The sympathetic nerve. This nerve confers vitality on all the important portions of the system. It exerts a controlling influence over the involuntary functions of digestion, absorption, secretion, circulation, and nutrition. Every portion of the body is, to a certain extent, under its influence, as filaments from this system of nerves accompany the blood-vessels throughout their course.
792. An important use of the sympathetic nerve is to form a communication of one part of the system with another, so that one organ can take cognizance of the condition of every other, and act accordingly. If, for example, disease seizes the brain, the stomach, by its sympathetic connection, knows it; and as nourishment would add to the disease, it refuses to receive food, and perhaps throws off what has already been taken. Loss of appetite in sickness is thus a kind provision of nature, to prevent our taking food when it would be injurious; and following this intimation, we, as a general rule, should abstain from food until the appetite returns.
What is the function of this nerve? What is the effect if the seventh pair is divided, or its function destroyed by disease? 791. What is said of the sympathetic nerve? 792. What is the use of the sympathetic system? Explain fig. 133.
Note. Let the anatomy and physiology of the nervous system be reviewed from figs. 131, 132, 133, or from anatomical outline plate. No. 8.
HYGIENE OF THE NERVOUS SYSTEM.
793. As the different organs of the system are dependent on the brain and spinal cord for efficient functional action, and as the mind and brain are closely associated during life, the former acting in strict obedience to the laws which regulate the latter, it becomes an object of primary importance in education, to discover what these laws are, that we may escape the numerous evils consequent on their violation.
794. For healthy and efficient action, the brain should be primarily sound; as this organ is subject to the same general laws as other parts of the body. If the brain of the child is free from defects at birth, and acquires no improper impressions in infancy, it will not easily become diseased in after life. But, if the brain has inherited defects, or has acquired a proneness to disease by mismanagement in early life, it will more easily yield to influences that cause diseased action. The hereditary tendency to disease is one of the most powerful causes that produce nervous and mental affections. Consequently, children have a strong tendency to the diseases from which the parents suffered.
795. When both parents have similar defects, or have descended from tainted families, the children are usually more deeply impressed with their imperfections than when only one possesses the defect. This is the reason of the frequency of nervous disease and imbecility among the opulent, as intermarriages among near relations are more frequent with this class than among the poor.
793-850. Give the hygiene of the nervous system. 793. Why is it important to know the laws which regulate the action of the brain? 794. What is necessary that the action of the brain be healthy and efficient? What follows if the brain of the child has inherited defects? 795. What is the effect when both parents possess similar defects?
Observation. Among some of the reigning families of Europe, particularly the Spanish, the folly of intermarriage among themselves is strongly illustrated. The high and noble talents that characterized their progenitors are not seen, but there is now exhibited, among their descendants, imbecility and the most revolting forms of nervous disease.
796. "Unhappily, it is not merely as a cause of disease, that hereditary predisposition is to be dreaded. The obstacles which it throws in the way of permanent recovery are even more formidable, and can never be entirely removed. Safety is to be found only in avoiding the perpetuation of the mischief."
797. "Therefore, if two persons, each naturally of excitable and delicate nervous temperament, choose to unite for life, they have themselves to blame for the concentrated influence of similar tendencies in destroying the health of their offspring, and subjecting them to all the miseries of nervous disease, madness, or melancholy." The command of God not to marry within certain degrees of consanguinity, is in accordance with the organic laws of the brain, and the wisdom of the prohibition is confirmed by observation.
Observation. The inhabitants, females particularly, of the sea-girt islands of America, are more affected with nervous diseases, than those who reside upon the mainland. The prevalence of these affections is ascribed to the frequent intermarriage of persons closely related by blood.
What is one cause of nervous disease among the higher classes? What is true of some of the reigning families of Europe? 796. Why is hereditary predisposition to be dreaded? 797. Is the prohibition of God respecting intermarriage in accordance with the organic laws of the brain? What is said of the inhabitants of the sea-girt islands of America?
798. The brain requires a due supply of pure blood. This organ receives an unusually large supply of blood, in comparison with the rest of the body. It is estimated that one tenth of all the blood sent from the heart goes to this organ. If the arterial blood be altogether withdrawn, or a person breathes air that is filled with carbonic gas, the brain ceases its proper action, and sensibility with consciousness becomes extinct.
Illustrations. 1st. If a person lose a considerable quantity of blood, dizziness and loss of consciousness follow. This results from the brain not receiving a sufficient amount of blood to sustain its functions.
2d. When an individual descends into a well or pit that contains carbonic acid, the blood is not changed or purified in the lungs, and loss of consciousness and death soon follow.
799. The slighter variations in the state of the blood have equally sure, though less palpable effects. If its vitality is impaired by breathing an atmosphere so much vitiated as to be insufficient to produce the proper degree of oxygenation, the blood then affords an imperfect stimulus to the brain. As a necessary consequence, languor and inactivity of the mental and nervous functions ensue, and a tendency to headache, fainting, or hysteria, makes its appearance.
Observations. 1st. Let a person remain, for a time, in a crowded, ill-ventilated, hall or church, and headache or faintness is generally produced. This is caused by the action of impure blood upon the brain.
2d. If a school-teacher wishes to have his pupils, on the day of examination, appear creditably, he will be careful to have the room well ventilated. Ventilating churches might prevent the inattention and sleepiness that are observed during the afternoon service.
798. Why does the brain require a due supply of pure blood? What is the effect when a person loses a considerable quantity of blood? What causes the loss of consciousness when carbonic acid is breathed? 799. What effects are produced by slight variations in the quality of the blood? From the following observations, give some of the effects of impure blood on the brain.
3d. In many instances, the transmission of imperfectly oxygenated blood to the brain, is an influential cause in the production of nervous disease and delicacy of constitution. The only efficient remedy for these conditions is a supply of pure blood to the brain.
800. The brain should be called into action. This organ, like the muscles, should be used, and then allowed to rest, or cease from vigorous thought. When the brain is properly called into action by moderate study, it increases in size and strength; while, on the other hand, if it is not used, the action of this organ is enfeebled, thereby diminishing the function of all parts of the body.
801. The brain, being an organized part, is subject, so far as regards exercise, to the same laws as the other organs of the body. If it is doomed to inactivity, its size diminishes, its health decays, and the mental operations and feelings, as a necessary consequence, become dull, feeble, and slow. If it is duly exercised after regular intervals of repose, the mind acquires readiness and strength. Lastly, if it is overtasked, either in the force or duration of its activity, its functions become impaired, and irritability and disease take the place of health and vigor.
802. The consequences of inadequate exercise will first be explained. We have seen that by disuse the muscles become emaciated, the bones soften, and the blood-vessels are obliterated. The brain is no exception to this general rule. It is impaired by permanent inactivity, and becomes less fit to manifest the mental powers with readiness and energy. Nor will this surprise any reflecting person, who considers that the brain, as a part of the same animal system, is nourished by the same blood and regulated by the same vital laws as the muscles, bones, and arteries.
800. Why should the brain be called into action? 801. What is the effect if the brain is doomed to inactivity? 802. Show the consequences of disuse of the organs mentioned in preceding chapters. Does the same principle apply to the brain?
803. It is the weakening and depressing effect which is induced by the absence of the stimulus necessary for the healthy exercise of the brain, that renders solitary confinement so severe a punishment, even to the most daring minds. Keeping the above principle in view, we shall not be surprised to find that non-exercise of the brain and nervous system, or, in other words, inactivity of intellect and feeling, is a very frequent predisposing cause of every form of nervous disease.
804. For demonstrative evidence of this position, we have only to look at the numerous victims to be found among females of the middle and higher ranks, who have no calls to exertion in gaining the means of subsistence, and no objects of interest on which to exercise their mental faculties, and who, consequently, sink into a state of mental sloth and nervousness, which not only deprives them of much enjoyment, but subjects them to suffering, both of body and mind from the slightest causes.
805. But let the situation of such persons be changed; bring them, for instance, from the listlessness of retirement to the business and bustle of the city; give them a variety of imperative employments, and so place them in society as to supply to their cerebral organs that extent of exercise which gives health and vivacity of action, and in a few months the change produced will be surprising. Health, animation, and energy, will take the place of former insipidity and dulness.
806. An additional illustration, involving an important principle in the production of many distressing forms of disease will be found in the case of a man of mature age, and of active habits, who has devoted his life to the toils of business, and whose hours of leisure have been few and short. Suppose such a person to retire to the country in search of repose, and to have no moral, religious, or philosophical pursuits to occupy his attention and keep up the active exercise of his brain; this organ will lose its health, and the inevitable result will be, weariness of life, despondency, or some other variety of nervous disease.
803. What renders solitary confinement so severe a punishment to the most daring minds? What is a predisposing cause of nervous disease? 804. In what classes do mental and nervous debility prevail? 805. How can this be counteracted? 806. Give another illustration, showing how disease of the brain is induced.
807. One great evil attending the absence of some imperative employment or object of interest, to exercise the mind and brain, is the tendency which it generates to waste the mental energies on every trifling occurrence which presents itself, and to seek relief in the momentary excitement of any sensation, however unworthy. The best remedy for these evils is to create occupation to interest the mind, and give that wholesome exercise to the brain, which its constitution requires.
808. The evils arising from excessive or ill-timed exercise of the brain, or any of its parts, are numerous. When we use the eye too long, or in too bright a light, it becomes bloodshot. The increased action of its vessels and nerves gives rise to a sensation of fatigue and pain, requiring us to desist. If we relieve the eye, the irritation gradually subsides and the healthy state returns. But, if we continue to look intently, or resume our employment before the eye has regained its natural state by repose, the irritation at last becomes permanent, and disease, followed by weakness of vision, or even blindness, may ensue.
809. Phenomena precisely analogous occur, when, from intense mental excitement, the brain is kept long in a state of excessive activity. The only difference is, that we can always see what happens in the eye, but rarely what takes place in the brain; occasionally, however, cases of fracture of the skull occur, in which, part of the bone being removed, we can see the quickened circulation in the vessels of the brain, as easily as those of the eye.
807. What is one great evil attending the absence of some imperative employment to exercise the mind and brain? What is the true remedy for these evils? 808. From what other cause do evils arise to the brain? Explain the evil of it by the excessive use of the eye. 809. What is the only difference in the analogy of the phenomena of the eye and brain? Has the analogy been verified?
810. Sir Astley Cooper had a young man brought to him, who had lost a portion of his skull, just above the eyebrow. "On examining the head," says Sir Astley, "I distinctly saw that the pulsation of the brain was regular and slow; but at this time he was agitated by some opposition to his wishes, and directly the blood was sent with increased force to the brain, and the pulsation became frequent and violent."
811. Indeed, in many instances, the increased circulation in the brain, attendant on mental excitement, reveals itself when least expected, and leaves traces after death, which are very perceptible. When tasked beyond its strength, the eye becomes insensible to light, and no longer conveys any impressions to the mind. In like manner, the brain, when much exhausted, becomes incapable of thought, and consciousness is almost lost in a feeling of utter confusion.
812. At any time of life, excessive and continued mental exertion is hurtful; but in infancy and early youth, when the structure of the brain is still immature and delicate, permanent mischief is more easily produced by injudicious treatment than at any subsequent period. In this respect, the analogy is as complete between the brain and the other parts of the body, as that exemplified in the injurious effects of premature exercise of the bones and muscles.
813. Scrofulous and rickety children are the most usual sufferers in this way. They are generally remarkable for large heads, great precocity of understanding, and small, delicate bodies. But in such instances, the great size of the brain, and the acuteness of the mind, are the results of morbid growth. Even with the best of management, the child passes the first years of its life constantly on the brink of active disease.
810. Relate the case detailed by Sir Astley Cooper. 811. May the increased functional action of the brain change its structure? 812. At what age particularly is excessive and continued mental exertion hurtful? 813. What is said of scrofulous and rickety children?
814. Instead, however, of trying to repress its mental activity, the fond parents, misled by the early promise of genius too often excite it still further, by unceasing cultivation, and the never-failing stimulus of praise. Finding its progress for a time equal to their warmest wishes, they look forward with ecstasy to the day when its talents will break forth and shed lustre on its name.
815. But in exact proportion as the picture becomes brighter to their fancy, the probability of its being realized becomes less; for the brain, worn out by premature exertion, either becomes diseased, or loses its tone, leaving the mental powers imbecile and depressed for the remainder of life. The expected prodigy is thus easily outstripped in the social race by many whose dull outset promised him an easy victory.
816. Taking for our guide the necessities of the constitution, it will be obvious that the modes of treatment commonly resorted to ought to be reversed. Instead of straining to the utmost the already irritable powers of the precocious child, and leaving his dull competitor to ripen at leisure, a systematic attempt ought to be made, from early infancy, to rouse to action the languid faculties of the latter, while no pains ought to be spared to moderate and give tone to the activity of the former.
817. Instead of this, however, the prematurely intelligent child is sent to school and tasked with lessons at an unusually early age, while the healthy but more backward boy, who requires to be stimulated, is kept at home in idleness, perhaps for two or three years longer, merely on account of his backwardness. A double error is here committed. The consequences to the intelligent boy are, frequently, the permanent loss both of health and of his envied superiority of intellect.
814. How are such children usually managed? 815. What is the cause of their early promise and subsequent disappointment? 816. What mode of treatment should be adopted in educating precocious children? 817. How should the dull or less active child be treated? What is the usual course?
818. In youth, too, much mischief is done by the long daily period of attendance at school, and the continued application of the mind which the ordinary system of education requires. The law of exercise—that long-sustained action exhausts the vital powers of the organ—applies as well to the brain as to the muscles. Hence the necessity of varying the occupations of the young, and allowing frequent intervals of exercise in the open air, instead of "enforcing the continued confinement now so common."
Observation. It is no unusual occurrence, that on examination day, the best scholars appear indifferently. This may be the result of nervous exhaustion, produced by extra mental effort in preparing for the final examination. It is advisable for such pupils to divert their minds from close study for a few days previous to examination. During this time, the student may indulge in physical recreation, social intercourse, and a moderate amount of reading.
819. "In early and middle life, fever, an unusual degree of cerebral disorder, is a common consequence of the excessive and continued excitement of the brain. This unhappy result is brought on by severe study, unremitted mental exertion, anxiety, and watching. Nervous disease, from excessive mental labor and high mental excitement, sometimes shows itself in another form.
What are the consequences of the error? 818. What error prevails in the present system of education? Why should youths be allowed frequent intervals to exercise in the open air? Give observation. 819. What is a frequent consequence of continued and excessive excitement of the brain?
820. "From the want of proper intervals of rest, the vascular excitement of the brain has not time to subside. A restless irritability of temper and disposition comes on, attended with sleeplessness and anxiety, for which no external cause can be assigned. The symptoms gradually become aggravated, the digestive functions give way, nutrition is impaired, and a sense of wretchedness is constantly present, which often leads to attempts at suicide."
Observations. 1st. Moderation in mental exertion is more necessary in old age than in early or mature years. In youth and manhood, the exhaustion of the brain from over-excitement may be repaired, but no such result follows over-exertion in the decline of life. "What is lost then, is lost forever." At that period, the brain becomes excited, and is soon exhausted when forced to protracted and vigorous thought. Sir Walter Scott and President Harrison afford sad examples of premature death from overtasked brains at an advanced period of their lives.
2d. If the mind is incessantly engaged in the contemplation of the same object, there is danger from over-exertion of the brain at any period of life, but more particularly in old age. The more limited the sphere of mental action, the greater the danger of the brain being over-exercised. Hence the frequency of nervous diseases in poets, mathematicians, and musicians.
820. What often manifests itself from the want of proper intervals of rest? Why is moderation in mental action necessary in old age? What is the effect if the mind is incessantly engaged in the contemplation of the same object?
HYGIENE OF THE NERVOUS SYSTEM, CONTINUED.
821. Having pointed out the evils arising both from inadequate and from excessive mental exertion, it remains to direct the attention to some of the rules which should guide us in the exercise of the brain.
822. We should not enter upon continued mental exertion, or arouse deep feeling, immediately before or after a full meal. Such is the connection between the mind and body, that even in a perfectly healthy person, unwelcome news, sudden anxiety, or mental excitement, occurring soon after eating, will impede digestion, and cause the stomach to loathe the masticated food.
823. The worst forms of indigestion and nervous depression are those which arise from excessive mental application, or depressed feeling, conjoined with unrestrained indulgence in the pleasures of the table. In such circumstances, the stomach and brain react upon and disturb each other, till all the horrors of nervous disease make their unwelcome appearance, and render life miserable. Too many literary men and students know this from sad experience.
824. We should engage in intense study in the early part of the day. Nature has allotted the darkness of the night for repose, and for restoration by sleep of the exhausted energies of mind and body. In the early part of the evening, if study or composition be ardently engaged in, the increased action of the brain, which always accompanies activity of mind, requires a long time to subside. If the individual possesses a nervous temperament, he will be sleepless for hours after he has retired, or perhaps be tormented by unpleasant dreams.
822. Why should we not arouse deep feeling immediately before or after eating a full meal? 823. How are the worst forms of indigestion and nervous depression produced? What class of men know this from sad experience? 824. What evils arise from studious application at night?
825. It is, therefore, of great advantage to enter upon intense mental application early in the day, and to devote several of the hours which precede bedtime to entertaining conversation, music, and lighter reading. The vascular excitement previously induced in the brain by study, has then time to subside, and sound, refreshing sleep is much more certainly obtained. This rule is of great consequence to those who are obliged to undergo much mental labor.
Observation. The idea of gathering wisdom by burning the "midnight oil," is more poetical than profitable. The best time to use the brain is during the day.
826. The close student and the growing child need more sleep than the idler or the adult. As steep is the natural repose of all organs, it follows that the more the brain and other organs of the system are employed, the more repose they require. The organs of the child, beside sustaining their proper functions, are busy in promoting its growth. This nutritive process is attended with a certain degree of exhaustion. The impaired health of children often results from a disregard of this principle. But, on the other hand, an excess of sleep produces feebleness, by preventing the proper exercise of the mind as well as the body.
827. The length of time the brain may be advantageously used, is modified by many circumstances. The power of the brain in different persons to endure action, is various. This is modified by its primary character; by development and age; by habits of action; by the health of the cerebral organ and general system; by the moral feelings and other conditions.
825. Why should we engage in intense study in the early part of the day? 826. What persons require the most sleep? Why? 827. What is said relative to the length of time that the brain can be advantageously used? Give a condition that modifies the amount of mental labor.
828. The primary physical organization of some individuals is such, that they are enabled to endure with impunity an amount of mental labor that would disorder, if not destroy functionally, the cerebral organ of others differently constituted. Napoleon Bonaparte was of this number. There can be no fixed period for mental labor, that may be adopted as a rule for all persons whose systems are maturely developed. Much less is there a proper definite period for study, that is applicable to all children.
Observation. The practice of retaining pupils of all ages, from five to twenty years, in the school-room the same period of time, for the purpose of study, is not predicated upon any law of physiology. An exercise of three hours, with one or two recesses of ten minutes each, may profit the eldest class; two hours with a recess of ten minutes, the middle class; while one hour, or one hour and a half, with one recess, would be as long a period as the youngest pupils should be retained in the study-room at one session.
829. A person who is accustomed to muscular exertion will endure a longer period of physical toil than one who is not inured to it. So it is with mental labor. If the brain has been habituated to mental action and profound study, it will not be so soon fatigued as when not accustomed to such exertions; consequently, an amount of mental labor may be performed with impunity at one time, that would exhaust and cause serious disease of the cerebral organ at another.
Observation. Persons that commence a course of study at a late period in life, frequently evince their zeal at the commencement by poring over their books twelve or more hours each day. The progress of such students is soon arrested by physical and mental depression. In such instances, it would be more judicious to commence with only three or four hours' vigorous application each day, and gradually protract the period of study five or more minutes every successive day, until the brain may be called into vigorous action six or eight hours with impunity.
828. Why can there be no fixed period for mental labor? What is said of the practice of retaining pupils of all ages the same period of time in the school-room? 829. Show that the action of the brain is influenced by habit, as well as the muscular system. What suggestion to those persons that commence a course of study at a late period in life?
830. The amount of mental power is greatly influenced by the general health. Such is the intimate connection of the different parts of the system, particularly the digestive apparatus, with the cerebral organs, that except there be vigor of constitution, and freedom from disease, mental efforts will be feeble and of little avail.
Observation. The prevalent opinion, that individuals who are feeble or diseased may acquire a collegiate education, and thus become useful to themselves and the community, is very generally erroneous. Such persons should enter upon a daily and systematic course of physical training, and their labor should be in the open air, in order that the system may be invigorated and freed from disease.
831. The moral feelings exert a controlling influence over the functions of the muscular, digestive, and respiratory organs. They also exert an influence, perhaps, more powerful upon the nervous system. While fear and anxiety depress, hope and the enlivening emotions, facilitate the functional activity of the brain, and increase its power for mental exertion. By a proper and systematic education of the moral feelings, they are not only a source of happiness, and productive of right conduct, but aid in the culture of the intellect. Consequently, we should cultivate a feeling of hopeful trust in the future, and a firm reliance upon the laws which the Creator has given us for our guidance.
830. Show that the amount of mental power is modified by the general health. What is said of feeble persons acquiring a collegiate education? 831. Do the moral feelings exert a controlling influence over the principal functions of the system? What is the effect of a proper and systematic culture of the moral feelings?
832. Regularity is very important in exercising the moral and intellectual powers. Periodicity, or a tendency to resume the same mode of action at stated times, is peculiarly the characteristic of the nervous system. If we repeat any kind of mental effort every day at the same hour, we at last find ourselves entering upon it without premeditation when the time approaches. In like manner, if we arrange our studies in accordance with this law, and take up each in the same order, a natural aptitude is soon produced, which renders application more easy than by resuming the subjects as accident may direct.
Observation. When engaged in abstruse studies, it may be found advantageous to pursue others that are less difficult. The intense application of the brain, which is requisite in the one instance, is relieved by directing the attention to a study that requires less thought. By this change, there is mental relaxation attended with invigoration of the cerebral organ. Or, it may be explained by assuming, that the brain is composed of an aggregate of distinct organs, each of which is called into action in pursuing different studies.
833. Effective study is impossible if the powers of the brain are depressed. When the cerebral organ has been temporarily debilitated by protracted intellectual efforts, it is ineffectual to attempt any concentrated mental exercise. This condition of the nervous system is indicated by confusion of thought and inability to attain results that usually follow similar efforts. Mental rest in these cases is required.
Observation. Students frequently fail in solving mathematical problems when the mind is prostrated by continued and excessive effort to obtain a solution. Not unfrequently after a night's rest the problem is quickly solved, and the pupil thinks he "dreamed it out." The true explanation is rest invigorated the exhausted brain, which fitted it for vigorous and successful thought.
832. Why is regularity of great importance in exercising the moral and intellectual powers? What suggestion when pursuing abstruse studies? How explained? 833. When is effective study impossible? How is this condition of the nervous system indicated?
834. The intellect should not be cultivated to the neglect of the moral and physical powers. All the faculties require for their development regular exercise, alternated with intervals of rest. This is as necessary to the due development of the moral feelings of a child as in physical training and mental culture. Consequently, those schools are to be preferred in the education of youth, where the physical, intellectual, and moral faculties receive each day a due share of attention and culture.
835. The continuance of healthy and vigorous action in the matured physical, mental, and moral powers, requires frequent and regular action, alternated with rest, as much as in their development. Consequently, those who cultivate one or two of these faculties, to the neglect of the others, exhibit a marked deficiency of acuteness and vigor in those not exercised. This defect reacts on the powers that are vigorous, diminishing the energy and deteriorating all the other faculties of man.
Observations. 1st. If the principles before mentioned are true, the adult, as well as the child, should spend a part of each day in some proper physical employment; another portion should be appropriated to intellectual pursuits; while another should be sedulously devoted to the cultivation of the moral feelings.
2d. Disease of the corporeal system more frequently occurs when only one set of faculties is used than when all are equally employed. This is particularly true of nervous and mental disease, which follows and is caused by either high intellectual action, or intense moral emotions, without a due amount of physical exercise.
How is the "dreaming out" of problems explained? 834. What is said of the culture of the intellect? What schools are preferable in the education of youth? Why? 835. What is the effect of cultivating only one faculty of the mind? Give observation 1st. Observation 2d.
836. The brain can exercise its full force upon only one object at a time. If its energies are directed to two or more operations, neither will receive that full power of exertion that it would if only one object had engaged the mind. Although the brain will direct several operations at the same time when only slight mental effort is required, yet when one operation becomes difficult, or demands special attention of the mind, the other will be suspended. This is illustrated in social conversation while walking. Let it become necessary to concentrate the nervous power upon the motor organs, and the conversation declines or ceases.
837. In acquiring an education, or in pursuing any profession or trade, none of those influences that promote the proper functions of the body, and tend to increase physical ease, should be neglected. For, if the brain is occupied with disagreeable sensations, it cannot concentrate its power as effectively in the various employments of man.
Observations. 1st. The situation, ventilation, light, and warmth of a school-room, together with the arrangement of the benches, do much to influence the concentration or distraction of the operations of the mind. Let there be attached to the school-house a spacious yard planted with trees; let its architecture be attractive; let the windows be arranged with regularity, and not with the elevation of a convict's cell, and the benches, in every respect, be adapted to the different scholars, so that the position of each may be comfortable, and we mistake if there is not a greater improvement, in a given time, in such a school, than where there is an apparent disregard to the pleasure or comfort of the scholars.
836. What is the effect if the brain concentrates its energies on more than one object at a time? How illustrated? 837. What should be regarded in pursuing any employment? Why? What is said in reference to the arrangement of school-rooms?
2d. Mechanics' shops should receive as much attention, relative to their situation, light, warmth, &c., as school-rooms. If these are duly observed, the nervous influence transmitted from the brain to the muscles will be more stimulating, as well as more abundant; consequently, labor will be performed with less exhaustion.
838. Repetition is necessary to make a durable impression on the mind. "The necessity of judicious repetition in mental and moral education, is, in fact, too little adverted to, because the principle which renders it efficacious has not been understood. To induce facility of action in the organs of the mind, practice is as essential as it is in the organs of motion.
839. "In physical education we are aware of the advantages of repetition. We know that if practice in dancing, fencing, skating, and riding, is persevered in for a length of time sufficient to give the muscles the requisite promptitude and harmony of action, the power will be ever afterward retained, although little called into use; whereas, if the muscles have not been duly trained, we may reiterate practice at different intervals, without proportionate advancement. The same principle applies equally to the moral and intellectual powers, because these operate by means of material organs.
840. "According to this principle, it follows, that in learning a language or science, six successive months of application will be more effectual in fixing it in the mind and making it a part of its furniture, than double or treble the time, if the lessons are interrupted by long intervals. Hence it is a great error to begin and study, and then break off, to finish at a later period. The fatigue is thus doubled, and the success greatly diminished.
Of mechanics' shops? 838. Is repetition necessary to make a durable impression on the mind? Why? 839. How is it with physical education? 840. What follows, according to this principle?
841. "The best way is to begin at the proper age, and to persevere till the end is attained. This accustoms the mind to sound exertion, and not to fits of attention. Hence the evil arising from long vacations; and also the evil of beginning studies before the age at which they can be understood, as in teaching children the abstract rules of grammar, to succeed in which, implies in them a power of thinking, and an amount of general knowledge, which they do not possess."
842. The skull is susceptible of fractures from slight blows. This occurs most frequently when the blow is given on the side of the head above and anterior to the ear. Here the bone is very thin, and often quite brittle. For these reasons, no instructor, or any person, should punish a child by striking upon any portion of the head.
Observation. A few years since, a teacher in one of the Middle States gave a pupil a slight blow upon the head. It fractured the skull and ruptured a blood-vessel of the brain, causing a loss of consciousness, and finally death.
843. Concussion of the brain may be produced by blows, or by violently shaking a person. As the brain is of pulpy consistence, the atoms of which it is composed, and the circulation of blood in its minute vessels, may be disturbed by the vibration from a blow on the exterior of the skull-bones. This disturbance of the cerebral organ is attended with unpleasant sensations, dizziness, loss of memory and consciousness. These may be followed by headache and inflammation of the brain. Concussion of the brain, and the results above mentioned, may be produced by the sudden motion attendant on the violent shaking of a scholar. Consequently, a child should never be seized by the arm and shaken violently as a method of chastisement.
841. What is the best way of learning the sciences? 842. Why should not a child be struck upon any portion of the head? What observation in this connection? 843. How may concussion of the brain be produced? What is the effect of each upon the brain of the child?
Observation. Most persons have experienced a disagreeable sensation and dizziness, caused by falling from a slight elevation, or by jumping from a carriage. This is the result of a moderate concussion of the brain.
844. In injuries of the brain, from blows and falls, the symptoms are usually alarming, and all should possess some information for such contingencies. In general, such accidents are attended by insensibility; the skin and extremities are pale and cold, the pulse is very weak and feeble, and the circulation is less vigorous; the respiration, also, is less frequent and full.
845. When these symptoms exist, the individual, in the first instance, should be placed in pure air, and friction and dry warmth should be applied to the pallid and cold skin. This should be assiduously persevered in until heat and color are restored to the skin and limbs, and due action of the heart and arteries has been established. Mild stimulants may also be used internally, with much advantage. The sympathizing friends should not be permitted to stand about the patient, as they vitiate the air. There should be no bleeding until the skin and extremities become warm. Send for a surgeon without delay.
Give an instance where moderate concussion of the brain is produced. 844. What are the symptoms when the brain is injured from blows and falls? 845. What treatment should be adopted?
THE SENSE OF TOUCH.
846. SENSATION is the perception of external objects by means of the senses. There are five senses, namely, Touch, Taste, Smell, Hearing, and Vision.
847. TOUCH is the sense by which the mind becomes acquainted with some of the properties of bodies, and enables us determine whether their surfaces are smooth or rough, their relative temperature, and, to a certain degree, their form and weight.
848. Some physiologists make a distinction between the sense of touch and tact. Tact, or feeling, is more general, extending over the whole surface of the skin and mucous membranes, while touch exists chiefly in the fingers of man and in the noses of certain quadrupeds.
849. "In the exercise of these functions, tact is considered passive; as, when any part of the system comes into contact with another body, a sensation of its presence is given, without the exercise of volition. On the contrary, touch is active, and is exercised voluntarily, for the purpose of conveying to the mind a knowledge of the qualities or properties of the surfaces of bodies; as when we feel of a piece of cloth to ascertain its qualities, or a polished surface, to prove its smoothness."
850. In man, the hand is admirably adapted to the exercise of touch. "The fineness of the skin, its great sensibility, the species of cushion formed by the sub-cutaneous fat at the extremities of the fingers, the length and flexibility of these organs, and the capability of opposing the thumb to the fingers, like a pair of forceps, are so many conditions essentially favorable to the delicacy of this sense, and enable us to appreciate with exactitude the qualities of the bodies we may feel."
846. Define sensation. How many senses have we? 847-851. What is said of the sense of touch? 847. Define touch. 848. What is the difference between touch and tact? 849. In the exercise of these functions, which is active, and which passive? 850. Why is the hand so admirably adapted to the exercise of the sense of touch?
851. The nerves that supply the sense of touch, proceed from the anterior half of the spinal cord. Where this sense is most acute and delicate, we find the greatest number of sensitive nervous filaments, and those of the largest size.
Observation. In amputating limbs, and other surgical operations, the division of the skin causes more pain than all the subsequent steps of the operation, however protracted. The muscles, cellular membrane, and fat have but little sensibility; while the bones, tendons, and ligaments are insensible when not diseased, and may be cut without causing pain.
HYGIENE OF THE SENSE OF TOUCH.
852. The sense of touch varies in different persons, and also in individuals of different ages. Thus the sensibilities of the child are more acute than those of the aged. Although there is an original difference of sensibility from organization, still, the function of the nerves of sensation is modified by certain influences.
853. The healthy or unhealthy, active or inactive state of the brain, influences the action of the sensitive nerves. In sound and perfect sleep, the brain is inactive. In this state, ordinary impressions made upon the skin are not observed by the sleeping person. Thus the arm may be blistered while sleeping, when exposed to the warm rays of the sun, and the individual will not be aware of it at the time.
851. From what do the nerves proceed that supply this sense? 852-864. Give the hygiene of the sense of touch. 852. Does this sense vary in different persons? 853. Mention a condition of the brain that influences the nerves of sensation.
854. If there is compression of the brain, as when the skull-bones are depressed, or disease of this organ exists, as in severe typhus fever, impressions made upon the nerves of the skin will not be noticed. The same is true when the mind is engaged in intense thought or study; heat or cold may be so intense as to disorganize the skin, and not to be noticed.
855. The varying health or condition of the brain usually depresses or increases the sensitiveness of the skin. This is seen in grief and fear, which diminish, while hope and joy increase the impressibility of this tissue. It is not uncommon to see the unfortunate insane endure exposure to heat and cold with seeming impunity; whereas it would induce almost insupportable suffering to the sane man. Diseases of the heart, stomach, and lungs, alter the condition of the brain, and modify, to a greater or less degree, the sensitiveness of the skin.
856. The state of the conducting nervous trunks influences the nerves of sensation. If a nervous trunk is compressed or divided, the parts supplied by nervous filaments from this branch, will be insensible to the impressions made upon them, and consequently such impressions are not transmitted to the brain.
Observation. When the inside of the arm or lower extremities rests upon a hard surface, the nerves may be compressed so as to deprive the parts of sensibility. This condition is called "numbness."
857. The quantity of blood supplied to the skin modifies its sensitiveness. If the quantity of blood is diminished, the sensibility of the skin will be impaired. This is demonstrated by noting the effects of cold upon the cutaneous tissue, the application of which contracts the blood-vessels, and drives the circulating fluid from this membrane, which is shown by the paleness, as well as by the shrivelled appearance of the skin. And, if this tissue is wounded while under the influence of cold, but little pain will be felt, and this chilling influence may be carried so far as not only to deprive the part of sensation, but of vitality.
854. Mention other conditions that affect these nerves. 855. What is the effect of the varying health or condition of the brain upon the sensitiveness of the skin? Give instances of this effect. 856. What is the result if a nervous trunk is divided or compressed? How may "numbness" in the limbs be produced? 857. Does the quantity of blood supplied to the skin affect its sensibility?
858. The influence of the blood upon the sensibility of the skin, is further demonstrated by the pain experienced when chilled extremities are suddenly exposed to heat. The nerves, by the sudden dilatation of the contracted blood-vessels, are put in vivid and rapid motion, which causes the painful and tingling sensation that we experience. In every part of the system, sudden changes produce unpleasant sensations, and frequently a diseased condition of the organs.
Observation. When the hands, or other portions of the body, are frozen, or severely chilled, safety and comfort demand that circulation be restored to the parts by moderate exercise in a cool room. Not unfrequently, the vitality of the limb is destroyed by immersing it in hot water or holding it near the fire.
859. The quality of the blood also influences sensation. If the brain and other parts of the nervous system receive impure blood, their energy is depressed, and the sensibility of the skin rendered more or less obtuse.
860. The condition of the cuticle modifies the impression made upon the cutaneous nerves. 1st. When the cuticle has become thick and hard, like horn, as on the inside of the mason's hand, it enables him to ply his tools without much suffering, because the thickened cuticle diminishes the impressions made upon the nerves.
How is it demonstrated? 858. How is the influence of the blood upon the skin further demonstrated? How should circulation be restored to limbs frozen or severely chilled? What should be avoided? 859. Show how the quality of the blood influences sensation. 860. Give the 1st condition of the cuticle that influences the impressions made on the cutaneous nerves.
861. 2d. When the cuticle is very thin and delicate, as on the hand of the lady who is unaccustomed to manual labor. Let her pursue some manual employment for several hours, and the extreme tenuity, or thinness of the cuticle, will not protect the nerves and parts below from becoming irritated and inflamed.
862. 3d. When the cuticle is removed by blistering or abrasion, the pain indicates that the naked nerves are too powerfully stimulated by the contact of external bodies. 4th. When the cuticle is coated with impurities, blended with the secretion from the oil-glands, the sensibility of the skin is lessened.
863. The sensibility of the cutaneous nerves is modified by being habituated to impressions. If, for example, an individual should immerse his feet in moderately warm water, at first it might induce a smarting sensation; in a short time, the nerves would not only become habituated to the warm water, but its warmth night be considerably increased. The same results follow, if an individual is exposed to a cold element. The impressions at first are highly disagreeable; but as soon as the nerves become accustomed to the surrounding atmosphere, it may impart the most agreeable sensations.
Illustration. 1st. Let a person from the tropical regions go to a colder climate, and the cool mornings of the latter will at first affect him unpleasantly; but, after a few days' exposure to the cooler air, the sensation will be far from disagreeable.
2d. Let a person enter a room moderately heated; gradually increase the temperature, until it attains extreme summer heat; not only the cutaneous nerves, but the whole system, become habituated to the high temperature. From these facts we learn that the sensations, are not always a correct index of the real temperature. A well-adjusted thermometer will indicate it with unerring certainty.
861. The 2d condition. 862. The 3d and 4th condition. 863. Show how habit influences the sensibility of the cutaneous nerves. Give illustration 1st. Illustration 2d.
864. Touch is modified, in a high degree, by education. Thus the blind, whose "windows of the soul" are closed to the beauties of the external world, cultivate this sense to such a degree that they can distinguish objects with great accuracy. And the rapidity with which they read books prepared for their use, is a convincing proof of the niceness and extent to which the cultivation of this sense can be carried.
Illustrations. 1st. The cloth-dresser, by the aid of this sense, distinguishes the quality, as well as the slightest difference of texture, in the different pieces of cloth.
2d. The miller, from a similar education, quickly detects the quality of flour or meal, by permitting it to pass between his fingers. The difference in the texture of cloths, or the quality of the flour, would not be distinguished by an individual whose tactile sense had not been trained to make nice comparisons.
864. Is this sense susceptible of improvement? What persons cultivate it to a high degree? Give illustration 1st. Illustration 2d.
SENSE OF TASTE.
865. The chief organ of TASTE is the upper surface of the tongue; though the lips, the palate, the internal surface of the cheeks, and the upper part of the oesophagus, participate in this function.
ANATOMY OF THE ORGANS OF TASTE.
866. The tongue is a double organ, composed chiefly of muscular fibres, which run in almost every direction. The two sides are so perfectly distinct, that sometimes, in paralysis, one side is affected, while the function of the other remains perfect. It possesses great versatility of motion, and can be moulded into a great variety of shapes. In articulation, mastication, and deglutition, the tongue is an auxiliary to other organs.
867. This organ is abundantly supplied with blood-vessels, having a large artery sent to each side of it. It is also very largely furnished with nerves; it receives nervous filaments from the fifth, ninth, and twelfth pairs of nerves. The branch of the fifth, called the gustatory, is the nerve of taste and sensibility; the twelfth, called the hypo-glossal, of voluntary motion. By means of the ninth, called the glosso-pharyngeal the tongue is brought into association with the fauces, oesophagus, and larynx. It is of obvious importance that these parts should act in concert; and this is effected by the distribution of this nerve.
 Some physiologists impute the sense of taste to the ninth pair of nerves; others, to the twelfth pair; while others, again, contend that taste is the result of a concurrent action of the fifth, ninth, and twelfth pairs of nerves.
865. What is the chief organ of taste? What other parts participate in the function? 866-870. Give the anatomy of the organs of taste. 866. Give the structure of the tongue. 867. Is this organ abundantly supplied with blood? From what source does the tongue derive its nerves?
868. What is the appearance of the surface of the tongue? Explain fig. 134.
868. The surface of the tongue is thickly studded with fine papillae, or vil'li, which give the organ a velvety appearance. These papillae are of three varieties. The first is situated near the base of the tongue. They belong to the class of mucous follicles. They are larger than the others, and are called len-tic'u-lar, from being shaped like a lens. These, together with the tonsils, (sometimes called the almonds of the ears,) secrete mucus, to lubricate the food in the act of deglutition.
869. The instruments of taste are the two other sets of papillae. One set consists of small, oval-shaped bodies, which are scattered over the whole surface of the tongue. They give it a rough appearance, and are called the fil'i-form papillae.
870. The other set of papillae is called the fun'gi-form. They are larger than the former, and consist of small, rounded heads, supported on short stalks, something in the shape of mushrooms, from which they derive their name. In the last two described sets of sensitive papillae, the gustatory branch of the fifth pair of nerves ramifies.
Observation. By applying strong acids, as vinegar, to the tongue, with a hair pencil, these points will become curiously lengthened.
PHYSIOLOGY OF THE ORGANS OF TASTE.
871. TASTE is the sense which makes us acquainted with the savor of substances. When fluids are taken into the mouth, the papillae dilate and erect themselves, and the particular impression excited is transmitted to the brain through filaments of the gustatory nerve. This sense is closely connected with that of smell. The pleasures derived from it are strictly sensual and corporeal, and contribute in no way to the expansion of the mind, like those of hearing and seeing.
How many varieties of papillae? Describe the first variety. What is the function of the lenticular papillae? 869. Describe the filiform papillae. 870. The fungiform papillae? What nerve ramifies in the fungiform papillae? How can these papillae, or points, be seen? 871-875. Give the physiology of the organs of taste. 871. Define taste.
872. If dry, solid food is taken, the tongue carries it to the back side of the mouth, where it receives secretions from the salivary glands; the saliva, becoming impregnated with its flavor, flows over the sides of the tongue, and gives to the papillae a perception of the savory juice; this impression is then communicated to the brain.
Observation. It is supposed that the salts which enter into the composition of the saliva, are very efficient agents in reducing substances to a proper state for making impressions on the nerves of taste. The fact that metals impart a peculiar taste, is owing to a galvanic shock, and not properly to what we understand by taste.
873. The primary use of taste is to guide animals in the selection of food, and to warn them against the introduction of noxious articles into the stomach. In all the inferior animals, we see that the original design of taste is still answered. But in man, this sense has been so abused and perverted, by the introduction of stimulants and condiments, and the endless admixture of different articles of food, that the simple action of this part seems to have been superseded almost entirely by acquired taste.
874. In children, this sense is usually acute, and their preference is for food of the mildest character. And it is also true, that every person has some peculiarities of taste, or dislikes to particular articles of food. This may be either constitutional or from the influence of association.
With what sense is this closely connected? What is said of this sense? 872. Give the process by which we taste substances. How can we account for the taste of metals when applied to the tongue? 873. What is the primary use of taste? Where do we see it perverted? 874. How is this sense in children? What is true of every person in reference to taste?
Observation. This sense has been made to vary more than any other by the refinements of social life. Thus, the Indian's like or dislike to particular kinds of food, generally extends to every person of the same tribe; but among civilized men, no two individuals can be found alike in all their tastes.
875. This sense is modified by habit, and not unfrequently those articles, which at first were disgusting, become highly agreeable by persevering in the use of them. By cultivation, this sense may be made very acute. Those persons whose business leads them to judge of the quality of an article by their taste, can discriminate shades of flavor not perceivable by ordinary persons. Epicures, and tasters of wines and teas, afford examples.
Observation. Many persons impair their taste by bad habits, as chewing and smoking tobacco, and using stimulating drinks, and pungent condiments with the food. These indulgences lessen the sensibility of the nerve, and destroy the natural relish for food.
What is true of the Indian? 875. Is this sense modified by habit? Give instances. How is this sense sometimes impaired?
SENSE OF SMELL.
876. This sense is located in the air-passages of the Nose. To understand the function of smell, the structure of the nose and nasal cavities, with the distribution of the olfactory nerves, must be first examined.
ANATOMY OF THE ORGANS OF SMELL.
877. The NOSE is composed of the Bones, Fi'bro-car'tilages, and Mu'cous Mem'brane, together with its integuments.
878. The BONES of the nose are the nasal, and the nasal processes of the upper jaw.
879. The FIBRO-CARTILAGES give form and stability to the framework of the nose, providing at the same time, by their elasticity, against injuries. They are five in number.
880. The MUCOUS MEMBRANE, which lines the interior of the nose, is continuous with the skin externally, and with the lining membrane of the parts of the throat. The entrance of the nostrils is provided with numerous hairs, which serve as guardians to the delicate membrane of the nose.
881. The NASAL FOSSAE, or nostrils, are two irregular, compressed cavities, extending from the nose to the pharynx. These cavities are bounded superiorly by the sphenoid and ethmoid bones; inferiorly, by the hard palate. In the middle line they are separated from each other by a bony and fibro-cartilaginous septum; upon the outer wall of each fossa, in the dried skull, are three projecting processes, termed spongy bones. In the fresh fossa, these are covered by a mucous membrane.
876. Where is the sense of smell located? 877-884. Give the anatomy of the organs of smell. 877. Name the parts that enter into the structure of the nose? 878. What bones form the framework of the nose? 879. What is the use of the cartilages? 880. What relation has the mucous membrane with other membranes of the nose? 881. Describe the nasal cavities.
882. The space that intervenes between the superior and middle spongy bone, is called the superior me-a'tus, or channel; the space between the middle and inferior bone, is the middle meatus; and that between the inferior bone and the floor of the fossa, is the inferior meatus.