324 P^'^S^^fi of the Vaccine Inoculation, and 



II. A conjlitution which has not undergone the fmall^^oXy 

 hut which has undergone the cow-pox, is unfufce^tible ofun^ 

 dergoing tbefmall~pox. 



III. A conjlitution which has not undergone the cow-pox, 

 hut which has undergone the fmall-pox, is unfufceptible of 

 undergoing the cow-pox. 



Now, if the variolous poifon deftroys the fufceptibility of the 

 conftitution to the future agency of this poifon, in the refpeft 

 of its producing the fmall-pox ; and if the cow-pox poifon 

 deftroys the fufceptibility of the conftitution to the fiiture 

 agency of the variolous poifon, in the refpeft of its pro- 

 ducing the fmall-pox ; and if the variolous poifon deftroys 

 the fufceptibility of the conftitution to the future agency of 

 the vaccine poifon, in the refpeft of its producing the cow- 

 pox J it feenis demonftrated, that the fame ftate of unfufcepti- 

 bility of the conftitution, with refpe6l to the future agency of 

 the variolous poifon, is produced equally by the agency of the 

 variolous poifon, and by the vaccine poifon. But if the va- 

 riolous poifon produces unfufceptibility of the conftitution to 

 the future agency of the vaccine poifon, and the vaccine poi- 

 fon produces unfufceptibility to the future agency of the va- 

 riolous poifon, it feems alfo demonftrable, that the following 

 4th propofition is true; viz. 



IV. A conjlitution which has undergone the vaccine dijeafe, 

 is unjufceptible of again undergoing that dif cafe from the agen- 

 cy of the vaccine poijm : becaufe a ftate of unfufceptibility, 

 with refpeft to the agency of the variolous poifon, is pro- 

 duced by the vaccine poifon {zd propoj.) ; and a ftate of 

 unfufceptibility, with refpeft to the agency of the vaccine 

 poifon, is produced by the variolous poifon {^d propoj.) : 

 but the ftate of the conftitution being the fame in the two 

 cafes, whether it be produced by the variolous or vaccine 

 poifon, with refpeft to tinrufceptihility, it feems inevitably, 

 in courfe, that unfufceptibility of the conftitution to the fu- 

 ture agency of tlae vaccine poifon is produced by the vaccine 



difcafe ; 



