HYDROPHOBIA. i 49 



the disease from animal to animal by inoculating into 

 the nervous system of the well animal a tiny portion 

 of nerve tissue from one which had succumbed. The 

 inoculated animals invariably died at a fixed period. 



After a long series of studies which we cannot here 

 review, he discovered that if the spinal cord of one 

 of the inoculated animals (rabbits) which had died 

 be dried in a clean place, it gradually lost its virulence, 

 so that whereas at first it invariably killed in seven 

 days, day by day it lost its power, so that after drying 

 for fourteen days it was quite inert. Given thus a 

 virus ranging gradually from the very feeble up to 

 the strongest, he saw the possibility of gradually ac- 

 customing the body to the stuff, so that at last it would 

 resist the very strongest. 



This was tried on dogs, and it was found that after 

 this gradual adaptation to the virus they became at 

 last wholly indifferent to the bites of mad dogs or 

 the artificial inoculation of the strongest virus. The 

 principle was finally applied to man, with the most 

 remarkable and satisfactory results. 



Rabies is peculiar in that a long period usually 

 elapses between the bite of a rabic animal and the 

 development of symptoms. This period, called the in- 

 cubation period, is in man on the average from thirty 

 to forty days; so that if the preventive treatment be 

 instituted without undue delay, there is usually time 

 for the adaptation of the subject to the artificial virus. 

 This accomplished, the disease does not occur. 



