Still dealing with the inflammatory exudation, the question arises whether all the cells found in it are derived directly from the blood. The origin of leucocytes as a whole is somewhat obscure. The bone-marrow, spleen, and lymphatic glands are usually regarded as their principal sources, but the connective tissue as a whole, which is intimately' related to the lymphatic system, is by many regarded as capable of giving origin to such cells. The study of the process of inflammation in connective tissues, and especially in such as possess no blood-vessels, seems to show that the connective tissue corpuscles are capable of giving rise to amoeboid cells. These, however, have not the character of the exuded leucocyte which, as we have seen, is of the polymorphonuclear variety. When examined in the tissues the nuclear distinction can generally be made out. Cells derived from the permanent tissues have probably more permanent characters than the exuded leucocytes.

Polymorphonuclear leucocytes in fibrinous reticulum.

Fig. 62. - Polymorphonuclear leucocytes in fibrinous reticulum. From a lung alveolus in pneumonia.

Hoffmann and Recklinghausen produced inflammation in the cornea and then excised the eye or the head of the animal and preserved it in a moist chamber. They found in two or three days that at the seat of irritation groups of amoeboid cells (pus corpuscles) had formed, as in ordinary keratitis. Then, also, several observers have described and figured the corneal corpuscles in inflammation, as drawing in their processes, and in doing so becoming amoeboid. They also leave detached portions of their protoplasm which become pus corpuscles. It has also been asserted that the epithelium on the posterior surface of Descemet's membrane, as well as that on the surface of the cornea and elsewhere becomes, at the outset of inflammations, amoeboid.

The so-called endogenous production of pus corpuscles is more doubtful. By this is meant the formation of these cells inside other cells. It has been asserted by Buhl, Rindfleisch, and others, that epithelial cells give origin in this way to pus corpuscles. No doubt the latter forms are sometimes found inside the former, but as both forms may be contractile, this does not imply that the one has given rise to the other, more especially as red corpuscles are found inside cells under similar circumstances.

The cells met with in inflammatory exudations are not all of the character of pus corpuscles. They are sometimes larger and partake of the character of derivatives of the epithelial cells. This is more particularly the case in certain inflammations of the lung, where the alveoli are frequently occupied by cells which are evidently produced from the epithelium of the alveoli (so-called catarrhal cells). A similar formation of cells is frequently seen in the uriniferous tubules in inflammations of the kidneys. (See under Parenchymatous Changes.) Again, in suppuration in epithelial structures generally, amoeboid cells are often found which are much larger than pus corpuscles and are derived from the epithelium. Neumann asserts that ciliated epithelium sometimes becomes amoeboid and can be recognized, even after it has become detached, by the persistence of some of its cilia.