varieties—the eosinophiles, lymphocytes, etc.—are less mobile and have still less marked phagocytic properties.
The roll-call of the phagocytic army would be a long task. The phagocytes are numerous in the sanguineous fluid, but are still six hundred and fifty times less so than the red corpuscles. They are almost as numerous in the lymph and the conjunctival tissue, where, besides occurring in their normal condition, they sport into a variety which appears to have abandoned its migratory habit, for a time at least, and into a giant variety one hundred times larger than the ordinary leucocytes, which M. Ranvier calls clasmatocytes. They are further found in such tissues as the skin and the mucous membrane, where, notwithstanding the cells are so crowded, they make their way into the intestine, and, by a sort of diapedesis (passage through the pores or interstices) called the phenomenon of Stoehr, toward all the free surfaces, whither exterior soluble substances invite them. As they go they destroy the microbes which, advancing in an inverse direction, would invade the organism and provoke an infection of intestinal origin.
The fact that this immense army of phagocytes is always in motion was first clearly recognized by Cohnheim, in 1867. He saw, in inflamed regions, where the vessels are gorged and distended, the white globules thrusting out a prolongation which seemed to pierce the wall, but in reality simply insinuated itself between its elements, and elongating itself, drew its entire body, as it were, through the narrow channel. This emigration, which is produced without making a break, through the pores and interstices of the vascular wall, has been designated diapedesis. It is ordinarily provoked by some foreign body, a pathogenic microbe, for instance, which has introduced itself into the place and spread its irritating secretion or cause of infection there. The phagocytes, attracted from the interior of the vessel, come up and devour the invader. But if they are incapable of dissolving it they bear it away to work their own ruin; they degenerate in their turn, become transformed into globules of pus, and the inflammation results in purulence. The study of the mechanism by means of which the leucocytes traverse the tissues is very interesting.
These remarkable wandering elements are found in all classes of animals, and in all present the same essential characteristics. They are more like free existences than the other cells living in society which compose the bodies of animals, and their history is substantially like that of the naked one-celled organisms. Their various functions and properties are of the highest interest in all departments of physiology. It has been demonstrated, in particular, that the white globules of the blood give rise to the most ener-