384 POPULAR SCIENCE MONTHLY. 



in changing from one stage of their existence to another, and in 

 tadpoles which lose their tails in becoming frogs; the old parts that 

 disappear are devoured by phagocytes. 



Especially in the case of infectious diseases has the protective 

 part performed by the leucocytary phagocytes been brought into 

 full view by M. Metchnikoff. He has shown that the white glob- 

 ules rush to meet the bacterides of inflammation that are introduced 

 through any wound, absorb them, and render them powerless to 

 do harm. In the lymphatic organs — the spleen, the lymphatic 

 ganglions, and the marrow — the white globules are normally accu- 

 mulated, and there is where the struggle is most active between 

 the bacterides of inflammation which are swarming in the blood 

 and the defensive agents of the organism. The same takes place 

 with the spirilla of recurrent typhus and the microbe of erysipelas. 



The leucocytes are capable of adapting themselves to conditions 

 different from those in which they usually live, provided the change 

 is not too abrupt. It may sometimes occur that the poison secreted 

 by a microbe will paralyze and kill the leucocyte, unless care has 

 been taken, by inoculations of virus, at first attenuated and after- 

 ward gradually increasing in virulence, to create an immunity in 

 the phagocyte, to make it refractory to the poison and capable of 

 swallowing the toxic bacterium without suffering from it. Expla- 

 nations have been sought in this property for the virtue of vaccina- 

 tion and the immunity that results from it, but they are evidently 

 only fragmentary, and there are other theories of immunity. 



The leucocytes are not always victorious over the microbes, 

 and when these excel in numbers or force it sometimes comes to 

 pass that they are overcome and succumb. Poisoned by the sub- 

 stance they have incorporated, they undergo a fatty degeneration 

 and become globules of pus. Pus is therefore formed of the ca- 

 davers of conquered leucocytes. Although that humor ought, for 

 the good of the system, to be rejected, like every other mortified 

 part, it is nevertheless true that the production of it is a beneficent 

 effort, and a salutary reaction of Nature against the morbid agent. 



It will be an enduring honor to the name of M. Metchnikoff 

 that he has revealed the importance of the function of phagocytes, 

 and has enriched science with a large number of new truths. A part 

 of this honor will be reflected upon the Pasteur Institute, which has 

 welcomed the eminent biologist for many years, and has intrusted 

 the direction of one of its services to him. The learned Kussian, 

 in creating the study of phagocytism, with its causes, mechanism, 

 and consequences, has opened a very extensive field of research to 

 which we have given only a distant and cursory glance. — Translated 

 for the Popular Science Monthly from the Revue des Deux Mondes. 



