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RELATION OF BUS AND MUCUS TO EPITHELIUM. 449

by the transuded fluid will also be found to consist of nothing but proliferating epithelium.

If now pus-, mucus- and epithelial cells be compared with one another, it appears that there certainly does exist a series of transitional forms, or intermediate stages, between pus-corpuscles and the ordinary epithelial structures. By the side of perfectly formed pus-corpuscles, provided with several nuclei, are very commonly found somewhat larger, round, granular cells with single nuclei, the so-called mucus-corpuscles (Fig. 11 B); a little farther on we see perhaps still larger cells of a typical form and with single, large nuclei, and these we call epithelial cells. But the epithelial cells are flat, angular, or cylindrical, whilst mucus- and pus-corpuscles under all circumstances remain round. Even from this circumstauce may be derived an explanation of the fact that, whilst the epithelial cells, which cover, and are in close apposition to, one another, acquire a certain firmness of cohesion, mucus and puscorpuscles which lie but loosely one against the other, and are of a spherical shape, retain a great degree of mobility and are easily displaced.

It has been said before now that mucus-corpuscles are nothing more than young epithelium; another step and pus-corpuscles would be nothing more than young mucuscorpuscles. This is a somewhat erroneous notion. It cannot be maintained that a cell, which up to the point when it becomes a so-called mucus-corpuscle has preserved its form as a spherical body, is still in a condition to assume the typical form of the epithelium, which ought to exist in the part; and just as little can it be said that a puscorpuscle, after it has developed itself in the regular manner, is capable of again entering upon a course of development calculated to produce a relatively permanent element of the body. The cells, in which the development of epithelial, mucus-, and pus-cells originates, are young forms, but they are not pus-corpuscles. In pus every new cell at a very early period sets about dividing its nucleus; after a short time the division of the nucleus reaches a high pitch, without any further growth on the part of the cell. In mucus the cells are wont merely to grow, and in some instances to become very large, but they do not pass certain limits, and above all they do not assume any typical form. In epithelium, on the contrary, the elements begin even at a very early period, to assume their particular form, for "what is to become a hook, right early gets a crook." The very youngest elements, however, which are found in pathological conditions, cannot be called epithelial cells, or at least they have as yet nothing typical about them, but are indifferent formative cells, which might also become mucus or pus-corpuscles. Pus-, mucus- and epithelial cells are therefore pathologically equivalent parts which may indeed replace one another, but cannot perform each other's functions.

Even from this it follows that the distinction which it has been sought to establish between mucus- and puscorpuscles, and for the discovery of which prizes were proposed in the last century, really could not be found out, and that the "tests" could never be otherwise than insufficient, inasmuch as the cells developed upon mucous membranes do not always possess a purely purulent, purely mucous, or purely epithelial character, but on the contrary in the great majority of cases a mixed condition exists. Nearly always, when a catarrhal process develops itself upon a large mucous surface, as, for example, in the urinary passages, quantities of puriform matter are produced, but its production is confined within certain limits, beyond which only mucus is secreted, and the secretion of mucus, also at some point changes into a formation of epithelium. This mode of suppuration must of course always have for its result, that, in places, where it reaches a certain height,

SUPPURATION IN CONNECTIVE TISSUE. 451

the natural coverings of the surface do not attain their full development, or that, where they possess a certain degree of solidity, they are removed and destroyed. A pustule on the skin destroys the epidermis, and so far we may assign a degenerative character to these forms of suppuration also.

But degeneration in the usual sense of the word, only occurs when deeper parts are attacked. This more deeply seated pus-formation regularly takes place in the connective tissue. In it there first occurs an enlargement of the cells (connective-tissue corpuscles), the nuclei divide and for some time multiply excessively. This first stage is then very soon followed by divisions of the cells themselves. Round about the irritated parts, where before single cells lay, pairs or groups of cells are subsequently found, out of which a new-formation of an homologous kind (connective tissue) usually constructs itself. More in the interior on the contrary, where the cells were early abundantly filled with nuclei, heaps of little cells soon appear, which at <

first still preserve the direction and forms of the previous connectivetissue corpuscles. Somewhat later we find here roundish collections, or diffuse "infiltrations," in which the intermediate tissue is extremely scanty and continually liquefies1 more and more, in proportion as the proliferation of the cells extends.

Fig. 137. Purulent granulation from the subcutaneous tissue of a rabbit, round about a ligature, a. Counective-tissue corpuscles. b. Enlargement of the corpuscles with division of the nuclei. c. Division of the cells (granulation), d. Development of the pus-corpuscles. 300 diameters.

'This liquefaction (and the same is true of the liquefaction we have described as occurring in bone, p. 420) is a purely chemical process; the collagenous (gelatine-yielding) substance is first transformed into mucus, and then, becoming converted into an albuminous fluid, liquefies.—From a MS. note by tie Author.

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If this process takes place beneath a surface which does not participate in the morbid change, the layers of epithelium are sometimes seen, still perfectly coherent, to run over the irritated and somewhat swollen part. The outermost layer of the intercellular substance is also often long preserved, whilst all the deeper parts of the connective tissue are already filled with pus-corpuscles, are "infiltrated," or "absceded"1 (abscedirt). At last the surface gives way, or without giving way is directly transformed into a soft, diffluent mass. This mode of suppuration gradually yields the so-called granulations which always consist of a tissue, where, in a small quantity of soft intercellular substance, more or less numerous, and, at least in the strictly proliferating stage of the granulations, round, cellular elements are imbedded. The nearer we come to the surface, the more do the cells, which in the deeper parts were mostly uni-nucleated, present divisions in their nuclei, and on the extreme confines they can no longer be distinguished from pus-corpuscles. Then a detachment of the epithelium is wont to take place, and finally it may be that the basissubstance liquefies and the individual elements are set free. If the proliferation continues abundant, the mass keeps constantly breaking up, the cells pour themselves out upon the surface, and a destruction takes place, which makes deeper and deeper inroads into the tissue, and throws up more and more of its cells upon the surface. This is an ulcer properly so-called.

According to the common notion, which supposed the pus to be derived from some exudation or other, this kind of ulceration was not at all easy of comprehension; people always found themselves obliged to assume a special kind of transformation in the tissue in addition to the suppuGRANULATION, ULCERATION. 453

1 i.e., converted into an abscess.—Travel.

ration, and at last they went so far as to attribute a certain chemical solvent power to pus. But by surgical experiments the conviction has long since been acquired in the most manifold ways that pus has no solvent power. Bones have been placed in cavities full of pus and left there for weeks, and when they were afterwards weighed, they had if anything become heavier, through the absorption of fluid matters, but no softening had been produced excepting that occasioned by decomposition. How far the tissue is destroyed by real solution, chiefly depends upon whether the basis-substance which surrounds the young cells, becomes completely fluid. If it retains a certain degree of consistence, the process is confined to the production of granulations, and these may just as well proceed from a surface whose continuity is perfect, as from one where there is a breach of it. In surgery it is generally assumed that granulations form upon the walls of the breach occasioned by a loss of substance, but in every case they arise directly out of the tissue. They are found directly seated upon bone without any loss of substance in it having preceded them. They are found also in direct contact with the cutis under the intact epidermis, and with mucous membranes. Only in proportion as they become developed, do the mucous membranes lose their normal character.

Every development of the kind gives rise, as it proceeds, to separate masses (foci—Heerde) of new tissue, just in the same way indeed that growing cartilage produces, in the immediate vicinity of the margin of ossification, those large groups of cells (Fig. 124.), each of which corresponds to a single pre-existing cartilage-cell. We have in fact to do with a process which finds its counterpart in the ordinary phenomena of growth. As a cartilage, when it does not calcify, as for example, in rickets, at last becomes so moveable that it can no longer perform its functions as ft supporting structure, so we see everywhere that the firm

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