232 THE CONTAGIOUS TYPHUS 



would have all died ; it would have been ne- 

 cessary to inoculate successively a number of 

 animals with the virus derived from the first 

 inoculation, and transmitted from an inocu- 

 lated animal to a healthy one, by which 

 means they would have acquired a virus of the 

 first, second, third generation, and so on. These 

 inoculations having always been made on four 

 animals at a time ; on two of them, the disease 

 would have been left to take its own course, 

 in order that the experimentalists might watch 

 its progress and development, and the two 

 others would have supplied the virus for 

 inoculation. 



At the third or fourth generation, the 

 virus, modified and attenuated in its infectious 

 principles, would no longer have been mortal 

 in its effects, as experience has proved in 

 Eussia. Then the inoculated animals, placed 

 under the control of hygienic cares and a few 

 purgative and tonic medications, would have 

 passed from convalescence to health. The 

 virus thus attenuated would have supplied the 

 means of a practical inoculation on a large 

 scale to all healthy animals. 



Proceeding thus, they would, moreover, but 



