THE THEORY OF PHAGOCYTOSIS. 495 



the following explanation. He admits that the immune-body 

 is fixed by the bacteria (or red corpuscles, as the case may be), 

 though he does not state that a chemical combination takes 

 place ; hence he calls it a fixative {fixateur). The immune- 

 bodies are to be regarded as auxiliary ferments {ferments adju- 

 vants') which aid the action of the alexine. Unlike the latter, 

 however, they are formed in excess during immunisation and 

 set free in the serum. He compares their action to that of en- 

 terokynase, a ferment which is produced in the intestine and 

 aids the action of trypsin. Thus, when the bacteria have fixed 

 the immune-body their digestion is facilitated either within the 

 phagocytes, or outside of them when the alexine has been set 

 free by phagolysis. He, however, maintains that extracellular 

 digestion or lysogenesis does not take place without the occur- 

 rence of phagolysis. The source of immune-bodies is, in all 

 probabihty, also the leucocytes, as they are specially abundant 

 in organs rich in these cells — spleen, lymphatic glands, etc. ; 

 here again the mononuclear leucocytes are probably the source 

 of the immune-bodies concerned in haemolysis, the polymorpho- 

 nuclear leucocytes the source of those concerned in bacteri- 

 olysis. . Although the immune-bodies are usually set free in the 

 serum, this is not always the case ; sometimes they are cofttained 

 in the cells, and this probably occurs when there is a high degree 

 of active immunity against bacteria without the serum having 

 an antibacterial action. In this way the facts of immunity can 

 be explained so far as these concern the destruction of bacteria. 



Metchnikoff's work has less direct bearing on the produc- 

 tion of antitoxins. He admits the fixation of the toxin by the 

 antitoxin to form a neutral compound, and he apparently con- 

 siders that leucocytes may also be concerned in the production 

 of antitoxins. Apart, however, from antitoxin formation, he con- 

 siders the acquired resistance of the cells themselves of high 

 importance in toxin immunity. 



When we consider Metchnikoff's theory as thus extended 

 to cover recently established facts, it must be admitted that it 

 affords a rational explanation of a considerable part of the 

 subject, provided that the changes in the chemiotactic phe- 

 nomena during immunisation are fully elucidated. It, however, 

 does not afford an explanation of the multiplicity and speci- 

 ficity of antitoxins as Ehrlich's does ; on the other hand, it is 



