372 BIOLOGY: GENERAL AND MEDICAL 



defense of the body against infection. His original ob- 

 servations were made upon certain water fleas invaded 

 by a fungus. In those cases in which the microparasite 

 was overcome, the phagocytic cells of the little animal 

 were so active that he attributed its salvation to them. 



Through years of patient investigation Metchnikoff 

 and his followers have brought together a tremendous 

 array of facts in support of the theory of phagocytosis, 

 and have entrenched themselves behind such conclusive 

 evidence as to be almost unassailable. 



FIG. 142. Phagocytosis; the omen turn, immediately after injection of 

 typhoid bacilli into a rabbit. Meshwork showing a macrophage, intermediate 

 forms, and a trailer, all containing intact bacilli. (Buxton and Torrey.) 



The theory naturally underwent many modifications 

 as necessity for them arose, but throughout the years of 

 enthusiastic appreciation that followed the development 

 of the lateral chain theory, Metchnikoff has remained 

 unshaken in the belief that the reactions of immunity 

 are simple and has continued to maintain that they are 

 all finally referable to the phagocytes. 



It becomes imperative, therefore, that the theory of 

 phagocytosis be carefully examined in order that its 

 merits as explanations of the phenomena of immunity 

 can be estimated. As originally conceived, phagocytosis 



