300 Pox. 



tiousness or susceptibility do not seem to corroborate this con- 

 ception. 



Although the disease occurs in man and in sheep in the 

 form of a severe general disease, and with an extensive pox 

 eruption, in cattle and goats eruptions are almost invariably 

 confined to certain parts of the bodies, their development being 

 associated with only very mild general symptoms. The disease 

 in man and sheep may very readily become epidemic, while 

 among other animals the infection is usually confined within 

 restricted limits. 



Very close relations exist undoubtedly hetvi een human and 

 cow pox. The vaccine of cow pox may be very readily inoculated 

 into man, but the inoculation produces only an eruption con- 

 fined to the point of inoculation, and never a general infection 

 analogous to variola. On the other hand human pox are less 

 surely transmissible to cattle. In some experimental cases 

 characteristic pox developed in cattle at the point of inoculation 

 (Numan, Ceely, Fischer, fiternod & Haccius, Simpson, Freyer, 

 Meder), in other cases only hard nodules developed after the 

 inoculation, which healed without changing into vesicles or 

 scabs (Chauveau) or again the inoculation remains entirely 

 negative (Ducamp & Pourquier obtained a positive result in 

 only one case, Juhel & Resnoy). 



These experimental observations appear to indicate that the 

 virus of human pox (Variola), and that of cow pox (Vaccinia) 

 are two different modifications of one and the same pox virus. 

 Fischer and Eternod & Haccius aimed to prove this by re- 

 inoculating man with pox lymph of calves which had been re- 

 peatedly inoculated with variola lymph, whereupon in several 

 thousand persons only a local pox eruption developed. From 

 the above findings these authors, as well as Roloff and Bollinger 

 conclude that variola may be changed into vaccinia by passage 

 through the body of cattle, and that therefore the vaccinia rep- 

 resents an attenuated modification of variola. That such a 

 transformation does however not easily and constantly result is 

 proven by the experiments of Chauveau, who after inoculations 

 of lymph from cows which were inoculated with variola virus, 

 repeatedly observed in man the development of pox as a severe 

 general affection. 



The very close relation between variola humana and variola 

 vaccinia is proven by the fact that vaccinia produces a lasting 

 immunity against variola. Inasmuch as the local affection 

 which develops after vaccination in man represents a very mild 

 form of human pox, vaccinia must be considered as an atten- 

 uated variola virus. If it is further considered that the trans- 

 mission of the contagion from man to man, as it has usually 

 been practiced in former times, produces in most cases only 

 a local affection, and further that pox in cows originally results 

 as a rule, and probably invariably, from transmissions from 



