RELATIONS OF SMALLPOX AND COWPOX. 461 



circumstances covvpox is obtained. He, however, only ex- 

 perimented on adult cows. The transformation has been 

 accomplished 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 reaction 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 smallpox 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 vario- 

 lation of calves. The criticism of these experiments which 

 has been offered, namely, that since many of them were per- 

 formed in vaccine establishments, the calves were probably 

 at the same time infected with vaccinia, is not of great 

 weight, as in all the recent cases at least, very elaborate 

 precautions have been adopted against such a contingency. 

 And at any rate it would be rather extraordinary that this 

 accident should happen to occur in every case. We can, 

 therefore, say that at present there is the very strongest 

 ground for holding not only that vaccinia confers immunity 

 against variola, but that variola confers immunity against 

 vaccinia. The experimentum crucis for establishing the iden- 

 tity of the two diseases would of course be the isolation of 

 the same micro-organism from both, and the obtaining of all 

 the results just detailed by means of pure cultures or the 

 products of such. In the absence of this evidence we are 

 at present justified in considering that there is strong reason 



