RELATIONS OF SMALLPOX AND COW POX, 501 



of conferring immunity against another. The most diffi- 

 cult question 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 experimented 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 ex- 

 periments 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 pro- 

 duced 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 variolation of 

 calves. The criticism of these experiments which has 

 been offered, namely, that since many of them were 

 performed in vaccine establishments, the calves were prob- 

 ably 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 extra- 

 ordinary 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 cruris for 

 establishing the identity of the two diseases would of 



