168 METCHNIKOFF'S VIEWS 



which occurs in these different situations. The site of the forma- 

 tion of an immune body will be referred to again. 



Thus, whilst Ehrlich sees in the substances taking part in 

 cytolysis evidence of the nutrition of the living molecules of cell 

 protoplasm, Metchnikoff sees in them ferments which were also, 

 in their first appearance in the animal economy, designed for the 

 elaboration of the nourishment of the body or of certain cells 

 therein, the difference being that, according to him, their primitive 

 function was the digestion of large particles as well as of molecules. 

 But in the highly-organized animals with which we have chiefly 

 to deal this function has been changed, for in them phagocytes do 

 not ingest bacteria and red corpuscles for the sake of the nourish- 

 ment they contain, but to rid the body of invaders ; the body as a 

 whole is nourished through the agency of other extracellular 

 digestive ferments, which are secreted into the alimentary canal. 

 It follows, therefore, that cytase is unnecessary in the circulating 

 blood, and, on this supposition, does not usually exist in that situa- 

 tion. Metchnikoff admits that immune body does so exist and has 

 indeed supplied a remarkable proof of the fact, since he showed 

 that the spermatozoa of immunized guinea-pigs are combined 

 with immune body, and only need the addition of fresh serum for 

 cytolysis to occur. Cytase and fixator, on MetchnikorPs explana- 

 tion of the phenomena, must be regarded as substances which in 

 the evolution of the animal kingdom were first developed as 

 digestive juices, but which now are entirely subservient to the 

 defence of the body against invaders. According to Ehrlich, they 

 are both in daily use in nourishment, and their defensive function 

 is of less importance than their value in cell nutrition. In either 

 case, the conception of immunity, as being fundamentally a process 

 of nutrition, is a most striking one. 



We have now to turn to a phenomenon which is of the highest 

 theoretical importance, and which bids fair to be of great practical 

 value in diagnosis. We have already referred to the fact that 

 Bordet, the chief advocate of the Unitarian theory of complement, 

 showed that if red corpuscles be sensitized with amboceptor and 

 added to fresh serum, the latter is deprived of all complementary 

 activity. The same phenomena occur with sensitized bacteria. 

 When, for instance, typhoid bacilli which had been acted on by 

 heated typhoid serum were added to fresh blood, allowed to act, and 

 then centrifugalized, it was found that the supernatant fluid had no 

 longer the power of dissolving red corpuscles sensitized by suitable 



