314 CLASSICS OF MODERN SCIENCE 



On December 6, 1883, a monkey was trephined and inoculated 

 with the bulb of a dog, which had itself been similarly inoculated from 

 a child who had died of rabies. The monkey took rabies eleven days 

 later, and when dead served for inoculation into a second monkey, 

 which also took the disease on the eleventh day. A third monkey, 

 similarly inoculated from the second one, showed the first symptoms 

 on the twenty-third day, etc. The bulb of each one of the monkeys 

 was inoculated, after trephining, into two rabbits each time. The 

 rabbits inoculated from the first monkey developed rabies between 

 thirteen and sixteen days, those from the second monkey between 

 fourteen and twenty days, those from the third monkey between 

 twenty-six and thirty days, those from the fourth monkey both of 

 them after the twenty-eighth day, those from the fifth monkey after 

 twenty-seven days, those from the sixth monkey after thirty days. 



It cannot be doubted after that, that successive passages through 

 monkeys, and from the several monkeys to rabbits, do diminish the 

 virulence of the virus for the latter animals ; they diminish it for 

 dogs also. The dog inoculated with the bulb of the fifth monkey 

 gave an incubation of no less than fifty-eight days, although it had 

 been inoculated in the arachnoid space. 



The experiments were renewed with fresh sets of monkeys and 

 led to similar results. We were therefore actually in possession of a 

 method by means of which we could attenuate the virulence of rabies. 

 Successive inoculations from monkey to monkey elaborate viruses 

 which, when transferred to rabbits, reproduce rabies in them, but with 

 a progressively lengthening period of incubation. Nevertheless, if 

 one of those rabbits be taken as the first for inoculations through a 

 series of rabbits, the rabies thus cultivated obeys the law which we 

 have seen before, and has its virulence increased at each passage. 



The practical application of those facts gives us a method for the 

 vaccination of dogs against rabies. As a starting point, make use of 

 one of the rabbits inoculated from a monkey sufficiently removed from 

 the first animal of the monkey series for the inoculation — hypodermic 

 or intra-venous — of that rabbit's bulb not to be mortal for a new 

 rabbit. The next vaccinal inoculations are made with the bulbs of 

 rabbits derived by successive passages from that first rabbit. 



In the course of our experiments we made use, as a rule, for inocu- 

 lation, of the virus of rabbits which had died after an incubation of 



