CHAPTER III

.

INFLAMMATION.

_Inflammation is an expression of the effort made by a given organism to rid itself of or render inert noxious irritants, arising from within or introduced from without_ (Sutton, modified).

After having duly considered hyperemia as a phenomenon having an identity and termination of its own, we are prepared to study the more complex processes included under the term _inflammation_, the first of which is the hyperemia already considered. The characteristic of the truly inflammatory process is that it does not stop with mere congestion nor with any of its previously mentioned terminations, but goes on to something more complex. It must be understood, therefore, in this consideration that hyperemia is the first act of the vessels, resulting from peculiar stimuli which will shortly be considered. Even the hyperemia seems to be now more distinct than under other circumstances, and, along with the dilatation of vessels and the stagnation of blood current, the capillary vessels seem crowded with blood corpuscles to an abnormal degree, the rapidity of their motion is checked, and there occurs accumulation of blood cells along the walls of the small veins, to which they seem to adhere as if by some new cohesive property. The result is that before long the vessel wall appears to have received a new coating of white corpuscles, this being more marked in the veins than in the arterioles, while in the latter the red are more numerously mingled with the white than in the veins, in which the distinction between the two classes of cells is better maintained.

Next comes the phenomenon whose clear recognition and description is inseparably connected with Cohnheim’s name. This is known under different names as _migration_ or _diapedesis of the leukocytes_. The program is about as follows: A little protrusion of the vascular wall, a marked alteration in the shape of a leukocyte, which yet adheres to this point of its lumen, and then the curious fact so often seen under the microscope--the gradual passage of this cell through the vascular wall, from its inner to its outer side, by what is generally known as its _ameboid movement_. This migration of the leukocyte is not confined to its mere escape from the restriction of the vessel lumen, but goes on to an indeterminate extent after it has detached itself from the outer surface of the vessel. This seems to occur by virtue of the same ameboid characteristic which it exhibited in passing through between the cells of the vessel itself. If this occurs at one point, it occurs at innumerable points, in consequence of which a large number of leukocytes escape into the tissues of the part involved. This diapedesis occurs most markedly from the smaller veins, to a less extent from the capillaries. The cells which escape from the latter are usually accompanied by red cells, the consequence being that the exudate which necessarily occurs at the same time is more or less tinged with the coloring matter of the blood, and is known as a hemorrhagic exudate.

The above phenomenon, described in so few words, is in its minutiæ a really complex one, depending on a variety of causes not easily appreciated; but it is at least positive and well known, because it can be observed at will in the mesentery or web or tongue of certain animals which can be confined upon the stage of the microscope. The _phenomena of inflammation_, therefore, comprise, first, _hyperemia_, and then _escape_ from the bloodvessels of the _corpuscular_ and _fluid_ elements of the blood. The former may be due, as already seen, to various irritations of a non-specific character; while, as we shall learn, the latter practically never take place save when the irritation has been, as pathologists say, specific or infectious.

The phenomena of true inflammation comprise practically the roles played by the three elements which conspire to produce those changes--namely, the _tissues_, the _blood_, and the _specific irritants_ which are the primary cause of the entire lesion. Each of these should be considered separately.

All observers agree that in actively inflamed tissues the number of cells is very greatly increased. A certain increase may be accounted for by that which has already been described--namely, the escape into the tissues of the wandering cells from the bloodvessels. But neither this alone nor the products of their rapid proliferation are sufficient to account for all the cells found in the truly inflammatory condition. It is now well established that in connective tissue there are two varieties of cells--the fixed and the wandering--the former concealed in the trabeculæ of the intercellular substance, while the latter are small, ordinarily round in shape, much resembling the white corpuscles, possessed of ameboid characteristics, and having the power of changing position. These are known as the wandering cells, which meander through the lymph spaces of the tissues or back and forth into and out of the blood-vascular system, their migration being regulated by causes not yet known. Under natural conditions their number is relatively small. Once given a true inflammatory disturbance they are reproduced with amazing rapidity; and their numbers, added to those produced by diapedesis of leukocytes, with the combined proliferative activity of both forms, serve to account for the new cells whose presence characterizes phlegmonous and other similar disturbances. That these wandering connective-tissue cells have much to do with these changes is shown by the unmistakable evidences of excessive activity known as _karyokinesis_ (_i. e._, _nuclear activity_).

Karyokinesis is common not only in inflammatory disturbances, but in new-growths of rapid formation, especially sarcomas, which are formed from mesoblastic cells, the same which have to do with connective tissue. Endothelial cells also undergo the same changes.

The peculiar characteristics of the leukocytes have already been described at considerable length in the preceding chapter. It must suffice, then, here to say that during the _inflammatory_ attack the leukocytes are _increased in number_, _i. e._, there is a temporary leukocytosis which is the usual accompaniment of suppuration. For instance, this is regularly present in purulent, but not in catarrhal, forms of appendicitis. The recognition of this fact may be of great value in diagnosis. For instance, leukocytosis is rarely present in tuberculous disease unless suppuration complicates the case. It is met with in suppurative osteomyelitis and in all cases of pocketing of pus. Moreover, when leukocytosis is present coagulability of the blood is increased. Of the various leukocytes, it is the mononuclear and polynuclear forms (see