THE PRiESENT EVOLUTION OF MAN— PHYSICAL 223 



of concentration that destroys or paralyzes untrained 

 cells of the same kinds. When Pasteur for his first 

 inoculation for the cure of rabies uses materials from 

 an old desiccated cord, the essentials of his injection 

 are not "waste products," but extremely attenuated 

 toxins — toxins so attenuated that the phagocytes, far 

 from being destroyed or paralyzed, react in response to 

 the stimulation from them, and are thereby placed in 

 a position of such advantage, that instead of being 

 destroyed they are able to react in a similar manner 

 to the stimulation of the more virulent toxins and the 

 microbes producing them of the next inoculation, where- 

 by they attain a position of still greater advantage, and 

 are able to withstand and react to the stimulation of 

 the toxins of the third injection, and so on in succession 

 till the toxins of the most virulent injection, which 

 would otherwise have destroyed or paralyzed them, to 

 which they could not have reacted at one effort, pro- 

 duce no other effect than another reaction of like kind, 

 by virtue of which they are able to withstand those 

 toxins, and to attack and destroy the micro-organ- 

 isms that produce them. Rabies, as we know, is of 

 slow development in man — i. e. the microbes increase 

 slowly in him, or at the least they produce their toxins 

 slowly in him, one or both, for it is not till weeks or 

 months after infection that he exhibits the charac- 

 teristic symptoms of the disease. This long incubation 

 period renders possible the success of the scientist 

 in his endeavours to save life — affords time during 

 which he is able to train the phagocytes to successful 

 battle. 



Syphilis resembles rabies in its slow development, 

 and therefore as regards it also we may hope or expect 

 that means will be found of attenuating the virus, 

 perhaps by passing it through a series of resistant 

 animals, or better still, by subjecting a pure culture, if 



