Acquired immunity against micro-organisms 299 



tlierebyand remain alive. This interpretation is certainly very ingenious, 

 but nothing proves that it corresponds with the real state of things. 

 Neisser and Wechsberg have themselves observed that the serum 

 of the normal goat can also prevent the bactericidal action of the 

 cytase. In this case, however, they suggest the intervention of an 

 anticytase of this normal serum. The same explanation might 

 perhaps serve also to explain the preventive action of the serum of 

 immunised animals. We know that anticytases are found frequently 

 enough in the various serums and that they undergo great variations, 

 according to the conditions present in the animals furnishing the 

 blood. 



In any case, it is evident that the theory of receptors must in 

 no way be regarded as the antithesis of the theory of phagocytosis. 

 This latter quite retains its right to affirm that, in acquired im- 

 munity against micro-organisms, phagocytes play the most general 

 and important part. They hold back the cytases which are 

 capable of ridding the animal of micro-organisms from destroying 

 them. It is further these same cells that produce and excrete the [314] 

 fixative and protective substances. The free fixatives may attack the 

 micro-organisms in the body fluids but they are incapable of depriv- 

 ing them of life or even of virulence. The cytases, after escaping 

 from the phagocytes, may certainly, in collaboration with the fixatives, 

 destroy a certain number of the micro-organisms, but only in special 

 cases met with, no doubt, but only rarely, under natural conditions. 

 On the other hand, the phagocytes in the animal which enjoys 

 acquired immunity constantly fulfil the function of seizing the 

 micro-organisms and of submitting them in their interior to the 

 combined action of fixatives and cytases. 



Acquired immunity, like natural immunity against micro-organisms, 

 presents merely special phases of intracellular digestion. 



