All the other characteristics of the white globules flow from these two of mobility and phagocytism, the significance of which has been set in a clear light by M. Metchnikoff. These characteristics are the attributes of the most primitive types of animal life. They appertain to cells not yet differentiated, to the unicellular organisms which occupy the first stages of life. They translate the vital energy of elements still independent and isolated, without definite place in the social organization and as yet without special high function, but for that very reason better adapted to the needs of the simplest animality. Their voracity is useful for the preservation of the social organism. By eliminating old, exhausted, diseased cells they rejuvenate the structure and prepare the way for new generations. And when the fecundity of these is exhausted the leucocytes come in to occupy the vacated situations, and conduct the organism thus patched up through a senile degeneracy to natural death. The leucocytes, white globules, or phagocytes, by virtue of their mobility, are found everywhere--in the blood, in all the organs, and in all parts of the body--but are perhaps most abundant in the blood. The study of them proceeds slowly, and we are still engaged in distinguishing the varieties among them. The most abundant and best known of them--those which answer most closely the description we have given--are those called the polynuclear, neutrophilous leucocytes. They are colored with neutral hues, and have a nucleus like a rolled-up scroll in structure. Other 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.