THE SCAVENGERS OF THE BODY. 381 



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 mem- 

 brane, 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, ad- 

 vancing 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 dis- 

 tended, 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 inter- 

 stices 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 phago- 

 cytes, attracted from the interior of the vessel, come up and de- 

 vour 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 inflamma- 

 tion 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 foimd 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 particu- 

 lar, that the white globules of the blood give rise to the most ener- 



