PASTEUR'S OBSERVATIONS 



165 



But these inoculations of saliva sometimes failed 

 to produce the disease ; and, when they succeeded, 

 the incubation-period was wholly uncertain : it 

 might be some months before the disease appeared. 

 Thus Pasteur was led to use, instead of the saliva, 

 an emulsion of the brain or spinal cord ; because, 

 as Dr Duboue* had suggested, the central nervous 

 system is the chief seat, the locus eleclionis, of the 

 virus of rabies. But these inoculations also were 

 not always successful, nor did they give a definite 

 incubation-period. 



Therefore he followed with rabies the method 

 that he had followed with anthrax. As he had 

 cultivated the virus of anthrax, by putting it where 

 its development could be watched and controlled, so 

 he must put the virus of rabies in the place of its 

 choice. It has a selective action on the cells of the 

 central nervous system, a sort of affinity with them ; 

 they are, as it were, the natural home of rabies, the 

 proper nutrient medium for the virus : therefore the 

 virus must be inoculated not under the skin, but 

 under the skull. 



These sub-dural inoculations were the turning- 

 point of Pasteur's discovery. The first inoculation 

 was made by M. Roux : — 



" Next day, when I informed Pasteur that the 

 intracranial inoculation offered no difficulty, he was 

 moved with pity for the dog. ' Poor beast, his 

 brain is doubtless injured : he must be paralysed.' 

 Without reply I went clown to the basement to 

 fetch it, and let it come into the laboratory. 

 Pasteur did not like dogs, but when he saw this 



