218 THE PRESENT EVOLUTION OF MAN— PHYSICAL 



unchanged in the blood and tissues. Pasteur's memorable 

 experiments on rabies were held to confirm this view. 

 It was thought that his thoroughly desiccated cords 

 contained the waste products, but not the living 

 organisms of hydrophobia, and that the rationale of 

 his treatment of that disease lay in dispx'oportionately 

 increasing the waste products as compared to the 

 microbes in the blood and tissues of the infected 

 person. 



■ There is perhaps a modicum of truth in this theory, 

 for the blood serum of animals which have acquired 

 immunity through illness against certain diseases — e. g. 

 cholera, erysipelas, anthrax, diphtheria, &c.^ — has greater 

 bactericidal power than the serum of animals yet 

 susceptible; but that the waste product theory is 

 utterly insufficient to account wholly for acquired 

 immunity is decisively proved by the fact that the 

 micro-organisms of certain diseases are able to flourisb 

 in the serum withdrawn from immune animals, which 

 should of course contain the waste products if they 

 exist in them. The anthrax bacillus is a case 

 in point, and it has been found, moreover, that this 

 micro-organism will live and grow in the anterior 

 chamber (in which there are normally no phagocytes) 

 of the eye of an immune animal, where also the waste 

 products if present in the animal should likewise be 

 present. A different interpretation of Pasteur's experi- 

 ments must therefore be sought. 



Pasteur furnished the key to the problem by some 

 other experiments. He found that the virus of rabies 

 is of constant strength in dogs. 



"And inoculations made from dog to dog kill the 

 animal with the same incubation period, the same 



1 Vuh Kantliack, British Medical Journal, February 20, 1892. 



