An inflammatory stimulus is a stimulus which acts either directly or through the medium of the blood upon the composition and constitution of a part in such a way as to enable it to attract to itself a larger quantity of matter than usual and to transform it according to circumstances. Every form of inflammation with which we are acquainted may be explained in this way. It may be assumed that inflammation begins from the moment that this increased absorption of matters into the tissue takes place, and the further transformation of these matters commences.
It must be noticed that hyperaemia is not the essential feature of inflammation, for inflammation occurs in non-vascular as well as in vascular parts, and the inflammatory processes are practically the same in both instances.
Nor is inflammatory exudation the essential feature of inflammation. I am of the opinion that there is no specific inflammatory exudation at all, but that the exudation we meet with is composed essentially of the material which has been generated in the inflamed part itself, through the change in its condition, and of the transuded fluid derived from the vessels. If, therefore, a part possess a great number of vessels, and particularly if they are superficial, it will be able to furnish an exudation, since the fluid which transudes from the blood conveys the special product of the tissue along with it to the surface. If this is not the case, there will be no exudation, but the whole process will be limited to the occurrence in the real substance of the tissue of the special changes which have been induced by the inflammatory stimulus.
In this manner, two forms of inflammation can be distinguished, the purely parenchymatous inflammation, where the process runs its course in the interior of the tissue, without our being able to detect the presence of any free fluid which has escaped from the blood; and the secretory (exudative) inflammation, where an increased escape of fluid takes place from the blood, and conveys the peculiar parenchymatous matters along with it to the surface of the organs. That there are two kinds of inflammation is shown by the fact that they occur for the most part in different organs. Every parenchymatous inflammation tends to alter the histological and functional character of an organ. Every inflammation with free exudation generally affords a certain relief to the parts by conveying away from it a great part of the noxious matters with which it is clogged.
I at present entirely reject the blastema doctrine in its original form, and in its place I put the doctrine of the continuous development of tissues out of one another. My first doubts of the blastema doctrine date from my researches on tubercle. I found the tubercles never exhibited a discernible exudation; but always organised elements unpreceded by amorphous matter. I also found that the discharge from scrofulous glands and from inflamed lymphatic glands is not an exudation capable of organisation but merely debris, developed from the ordinary cells of the glands.
Until, however, the cellular nature of the body had been demonstrated, it seemed necessary in some instances to postulate a blastema or exudation to account for certain new formations. But the moment I could show the universality of cells—the moment I could show that bone corpuscles were real cells, and that connective tissues contained cells—from that moment cellular material for the building of new formations was apparent. In fact, the more observers increased the more distinctly was it shown that by far the greater number of new formations arise from the connective tissue. In almost all cases new formations may be seen to be formed by a process of ordinary cell division from previously existing cells. In some cases the cells continue to resemble the parent cells; in other cases they become different. All new formations built of cells which continue true to the parent type we may call homologous new formations; while those which depart from the parent type or undergo degenerative changes we may designate heterologous. In a narrower sense of the word heterologous new formations are alone destructive. The homologous ones may accidentally become very injurious, but still they do not possess what can properly be called a destructive or malignant character. On the other hand, every kind of heterologous formation whenever it has not its seat in entirely superficial parts, has a certain degree of malignity, and even superficial affections, though entirely confined to the most external layers of epidermis, may gradually exercise a very detrimental effect. Indeed, suppuration is of this nature, for suppuration is simply a process of proliferation by means of which cells are produced which do not acquire that degree of consolidation or permanent connection with each other which is necessary for the existence of the body. Pus is not the solvent of cells: but is itself dissolved tissues. A part becomes soft and liquefies, while suppurating, but it is not the pus which causes this softening; on the contrary, it is the pus which is produced as the result of the proliferation of tissues.
A suppurative change of this nature takes place in all heterologous new formations. The form of ulceration which is presented by cancer in its latest stages bears so great a resemblance to suppurative ulceration that the two things have long since been compared. The difference between suppuration and suppuration lies in the differing duration of the life of different cells. A cancer cell is capable of existing longer than a pus corpuscle, and a cancerous tumour may last for months yet still contain the whole of its elements intact. We are as yet able in the case of very few elements to state with absolute certainty the average length of their life. But among all pathological new formations with fluid intercellular substance there is not a single one which is able to preserve its existence for any length of time—not a single one whose elements can become permanent constituents of the body, or exist as long as the individual. The tumour as a whole may last; but its individual elements perish. If we examine a tumour after it has existed for perhaps a year, we usually find that the elements first formed no longer exist in the centre; but that in the centre they are disintegrating, dissolved by fatty changes. If a tumour be seated on a surface, it often presents in the centre of its most prominent part a navel-like depression, and the parts under this display a dense cicatrix which no longer bears the original character of the new formation. Heterologous new formations must be considered parasitical in their nature, since every one of their elements will withdraw matters from the body which might be used for better purposes, and since even its first development implies the destruction of its parent structures.
In view of origin of new formations it were well to create a nomenclature showing their histological basis; but new names must not be introduced too suddenly, and it must be noted that there are certain tumours whose histological pedigree is still uncertain.
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 Azure transparent spheres conceived by the ancients to surround the earth one within another, and to carry the heavenly bodies in their revolutions.
 Book I., Prop. i. The areas which revolving bodies describe by radii drawn to an immovable centre of force do lie in the same immovable planes and are proportional to the times in which they are described.
Prop. ii. Every body that moves in any curve line described in a plane and by a radius drawn to a point either immovable or moving forward with a uniform rectilinear motion describes about that point areas proportional to the times is urged by a centripetal force directed to that point.
Prop. iii. Every body that, by a radius drawn to another body, howsoever moved, describes areas about that centre proportional to the times is urged by a force compounded out of the centripetal force tending to that other body and of all the accelerative force by which that other body is impelled.
 If the periodic times are in the sesquiplicate ratio of the radii, and therefore the velocities reciprocally in the subduplicate ratio of the radii, the centripetal forces will be in the duplicate ratio of the radii inversely; and the converse.
 i.e., showing convexity when in such a position as that, to an observer on the earth, a line drawn between it and the sun would subtend an angle of 90 deg. or thereabouts.
Variant spelling and punctuation have been preserved.