KELATIONSHIP OF SMALLPOX TO COWPOX 607 



observation is that it is questionable whether there are any 

 well-authenticated instances of one disease having the capacity 

 of conferring immunity against another. A question arising in 

 this connection is what happens when inoculations of smallpox 

 matter are made on cattle. Chauveau denies that in such 

 circumstances cowpox is obtained. He, however, only experi- 

 mented on adult cows. The transformation has been accom- 

 plished by many observers, including, in this country, Simpson, 

 Klein, Hime, and Copeman. The general result of these 

 experiments has been that if a series of calves is inoculated with 

 variolous matter, in the first there may not be much local 

 reaction, though redness and swelling appear at the point of 

 inoculation, and some general symptoms manifest themselves. 

 On squeezing some of the lymph from such lesion as occurs, and 

 using it to continue the passages through other calves, after a 

 very few transfers a local reaction indistinguishable from that 

 caused by cowpox lymph generally takes place, and the animals 

 are now found to be immune against the latter. Not only so, 

 but on using for human vaccination the lymph from such 

 variolated calves, results indistinguishable from those produced > 

 by vaccine lymph are obtained, and the transitory illness which 

 follows, unlike that produced in man by inoculation with small- 

 pox lymph, is no longer infectious. In fact, many of the strains 

 of lymph in use in Germany at present have been derived thus 

 from the variolation of calves. At present there is the strongest 

 ground for holding not only that vaccinia confers immunity 

 against variola, but that variola confers immunity against 

 vaccinia. In the absence of proof based on the isolation of 

 identical organisms from the two conditions we are at present 

 justified in considering that vaccinia and variola are the same 

 disease, and that the differences between them result from the 

 relative susceptibilities of the two species of animals in which 

 they occur naturally. 



With regard to the relation of cowpox to horsepox, it is 

 probable that they are the same disease. Some epidemics of 

 the former have originated from the horse, but in other cases 

 such a source has not been traced. Cattle-plague from the 

 clinical standpoint, and also from that of pathological anatomy, 

 resembles very closely human smallpox. Though each of the 

 two diseases is extremely infectious to its appropriate animal, 

 there is no record of cattle-plague giving rise to smallpox in 

 man or vice versa. When matter from a cattle-plague pustule 

 is inoculated in man, a pustule resembling a vaccine pustule 

 occurs, and further, the individual is asserted to be now 



