THE THEORY OF PHAGOCYTOSIS 497 



the breaking up of the cells the process known as phagolysis 

 and they then constitute the alexines, or complements of Ehrlich. 

 Of these, as has already been said, Metchnikoff thinks there 

 are probably two kinds one called macrocytase, contained in 

 the macrophages, which is specially active toward the formed 

 elements of the animal body, protozoa, etc. ; and the other, 

 microcytase, contained within the poly morpho-nu clear leucocytes, 

 which has a special digestive action on bacteria. It is the 

 microcytase which gives blood serum its bactericidal properties. 

 It appears to us, however, that Metchnikoff has gone too far in 

 distinguishing the activities of the two classes of cells so much 

 as he has done. 



When the properties of antibacterial sera, as above described, 

 are considered in relation to phagocytosis, Metchnikoff gives 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 (jfixateur). The immune-bodies 

 are to be regarded as auxiliary ferments (ferments adjuvants) 

 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 enterokinase, a 

 ferment which is produced in the intestine and which 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 occurrence of phagolysis. The 

 source of immune-bodies is, in all probability, also the leucocytes, 

 as these substances are specially abundant in organs rich in 

 such eells spleen, lymphatic glands, etc. ; here again the mono- 

 nuclear leucocytes are probably the source of the immune-bodies 

 concerned in haemolysis, the polymorpho-nuclear leucocytes the 

 source of those concerned in bacteriolysis. Although the im- 

 mune-bodies are usually set free in the serum, this is not always the 

 case ; sometimes they are contained in the cells, and this probably 

 occurs when there is a high degree of active immunity against 

 bacteria without a serum having an antibacterial action, the 

 powers of intracellular digestion being in such cases increased. 

 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 production 

 of antitoxins. He admits the fixation of the toxin by the anti- 

 toxin to form a neutral compound, and he apparently considers 

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