846 A NATO M Y [ANATOMY OF (Fig. 29), which arrange themselves iuto irregular meshes. In inflammatory diseases, and in the blood of pregnant women, the piles of corpuscles form more readily, and at the same time sink rapidly below the surface of the fluid, Fio. 29. 1, red corpuscles of healthy human blood; 2, rod corpuscles beginning to form rouleaux; 3, mesh-liku arrangement in healthy blood; 4, mesh-like arrangement in buffy blood, where the meshes are larger than in healthy blood. so as to cause the "buffy coat" seen in the blood coagulum. In the healthy blood of horses a buffy coat is formed as a natural condition of the coagulation. One of the most curious properties possessed by the living white blood corpuscle is that of protruding delicate processes from its circumference, which processes may change their shape, or be again withdrawn into the sub stance of the corpuscle, which then resumes its former circular outline. These processes resemble the sarcode prolongations which Amoeba and other Rhizopods can pro ject from various parts of their circumference ; and as a white blood corpuscle, like an Amosba, can by the move ments of the processes change its position, the term "amceboid movements" has been applied to the pheno mena in question. Like an Amosba, also, a white corpuscle can by these movements include within its substance minute particles of solid matter which it may come in contact with in its path. Thirty years ago W. Addison stated that the white blood corpuscles could pass through the walls of the blood-vessels into the surrounding tissue, where they formed mucus corpuscles, and, under certain pathological conditions, the corpuscles of pus or inflam matory lymph. The passage of white blood corpuscles through the wall of the capillaries was seen in 1846 by A. Waller; and though for many years his observations were ignored, yet the more recent inquiries of Cohnheirn and others into the subject have anew directed attention to them. It is now generally admitted that the migration of these corpuscles from the blood through the wall of the capillaries into the tissues does take place, and that they may then " wander " to and fro, owing to the mobility of their contractile protoplasm. These migrated corpuscles are also believed to play an important part in many physiological and pathological processes. But the blood contains, in addition to the red and white corpuscles, still more minute particles, which are, however, inconstant in number. Minute globules have been de scribed by Beale and Max Schultze, which are probably detached fragments of protoplasm budded off from the white corpuscles ; and Zimmermann has described, as elementary corpuscles, minute particles, which are appar ently derived from broken-up red corpuscles. In the very young embryo the blood corpuscles, like the capillary blood-vessels themselves, are formed by special differentiation of certain of the cells of the embryo, and these young corpuscles seem to have the power of multiply ing by fission. At first they are colourless, but afterwards assume a red colour. Even in mammals the earliest red blood corpuscles are nucleated and larger than the future red discs, but as development goes on, non-nucleated red corpuscles appear, and as their number increases, both absolutely and relatively with the progress of the foetus, in course of time all the nucleated red corpuscles have dis appeared, and are replaced by the non-nucleated discs. In adults the red corpuscles are believed to be derived from the white corpuscles, though the exact process of meta morphosis has not been satisfactorily ascertained. It is also believed that red corpuscles may be new-formed in the spleen, and Neumann has recently stated that the red marrow of the bones may serve as a centre of origin for the red blood corpuscles. In the foatus the liver apparently serves as a centre of origin for the white corpuscles, but its blood corpuscle forming function ceases at the time of birth. Throughout extra-uterine life the spleen and the lymphatic glands are without doubt organs of formation of the colourless corpuscles,--- those produced in the lymph atic glands, under the name of lymph corpuscles, being mingled with, the blood-stream where the fluid lymph flows into the venous system. When mixed with the blood, the lymph corpuscles become the white blood corpuscles. Corpuscles are also found in the blood of the invert e- brata. They are as a rule colourless, but E. Wagner pointed out that in the Cephalopoda they are coloured. They are sometimes round, at others oval or fusiform, and in worms and insects have even branched processes. They are always nucleated. THE LYMPH AND CHYLE. The lymph is the fluid found Lymp: in a subdivision of the vascular system named the lymph vascular system. It is transparent and colourless, and con tains numerous corpuscles floating in it, which correspond, in appearance, structure, and the possession of the pro perty of amoeboid movements, to the white corpuscles of the blood. The lymph corpuscles are formed in the glands situated in the course of the lymph vessels, and are carried away from the glands by the stream of lymph which flows through them. The chyle is a milky fluid found during the period of chyle. digestion in the delicate lacteal vessels which pass from the walls of the intestine. The lacteals join the lymphatics at the back of the abdomen to form the thoracic duct in which the lymph and chyle become mingled together. The chyle contains corpuscles similar to the lymph corpuscles, which are apparently derived from the lymph glands in the mesentery, through which the chyle flows on its way to the thoracic duct. The fluid of the lymph, the chyle, and the blood, in which the corpuscles are suspended, is some times described as a fluid intercellular substance. Cor puscles possessing the type of structure of the lymph corpuscles, are named lymphoid cells or leucocytes. Cells are also met with floating free in the secretions formed in the interior of some of the glands. They are more particularly found in the secretion of mucus from the mucous glands, and of saliva from the salivary glands. They are round, colourless, nucleated corpuscles, not unlike the white corpuscles of the blood, and have been detached from their original position in the gland follicles. 2d Group. Cells placed on Free Surfaces. By the term free surface is meant a surface which is not blended with or attached to adjacent structures, but is free or separable from them without dissection. Every free surface is covered by one or more layers of cells. Some times these cells are named an Epithelium, at others an Eudothelium. By the term Epithelium is meant the cells situated on free surfaces which are exposed either directly or indirectly to the air. By the term Endotheliuin is meant the cells situated on free surfaces which are not ex
posed either directly or indirectly to the air.
