564 Chapter XVII 



according to these writers, no co-operation by antitoxin is met with. 

 The body fluids of the goats do not become capable of neutralising the 

 toxin of the haemolytic serum, whilst the red corpuscles themselves 

 acquire an immunity against this toxin, an immunity entirely cellular. 

 Ehrlich attempted to penetrate into the essential mechanism of the 

 resistance of the red blood corpuscles on the supposition that these 

 corpuscles, instead of reproducing their receptors, as when there is 

 production of antitoxin, get rid of them entirely. Deprived of 

 receptors, they can no longer be affected by the haemolytic cytase 

 which, as Ehrlich maintains, only penetrates into the red corpuscles 

 owing to the affinity of the intermediate substance (fixative) for the 

 receptor. This hypothesis of the mechanism of acquired cellular 

 immunity scarcely accords with the hypothesis of the special function 

 attributed to the receptors in the nutrition of the living elements. 



Cellular immunity can be most easily demonstrated in relation to 

 the red corpuscles of the blood, as these elements are very numerous 

 and are capable of being isolated and freed from the fluid in which 

 they are bathed. For this reason, science does not as yet possess 

 sufficiently exact data on the immunity of other cells in higher 

 animals. ]Many facts, however, indicate that such immunity does 

 exist. There are, indeed, living elements which only acquire immunity 

 with great difficulty and very slowly. Such are the nerve cells, 

 elements which are specially susceptible. Von Behring has strongly 

 insisted on the fact that in animals subjected to repeated injections of 

 bacterial toxins, the nerve centres not only do not become accustomed 

 to their injurious action, but even acquire a hypersusceptibility which 

 is often very great. The observation is perfectly accurate, but it is none 

 the less true that this period of exaggerated susceptibility is followed 

 by another, during which the susceptibility becomes less marked and 

 ends by giving place to a true adaptation. We are, therefore, com- 

 pelled to accept the fact that even the nerve cells are no exception to 

 the general rule, but are able to acquire a diminished susceptibility to 

 a poison. 



Several facts of another series confirm this conclusion. In the 

 study of the action of the nervous system one frequently has occasion 

 to observe instances of adaptation. I will cite as an example 

 [589] the adaptation of animals to spinal concussion studied by Lepine^ 

 By percussing the lumbar region of rabbits and guinea-pigs we may 

 induce in them an immediate paraplegia. This is transitory, and 

 ^ Connpt. rend. Soc. de biol.y Paris, 1900, p. 385. 



