VAPJOLA VACCIX/E. 205 



matter, taken from a pock upon the body of a man who had 

 died of small-pox, into a cow's udder, and subsequently vacci- 

 nated some fifty persons with the matter derived from the cow. 

 Most of those so inoculated were attacked, not with vaccina but 

 with variola (small-pox), and three died. It is diflicult to 

 reconcile such a wdde difference in the results of experiments 

 seemingly carefully performed, but I am not prepared to admit 

 that the experiments of Chauveau and those of Martin have 

 satisfactorily proved that those of others were wrong. In 1836 

 Dr. Basil Thiele of Kasan, in South Eussia, inoculated some 

 cows on the udder with the virus of human small-pox, the result 

 being the production of vesicles bearing all the characteristics 

 of the true vaccine vesicle. The lymph so produced from the 

 variolation of the cows continued to retain the specific properties 

 of variola vaccinae throughout seventy-five successive trans- 

 missions to the human body ; and it is not stated that it had 

 lost its specificity after so many transmissions. 



In the face of such conclusive evidence, I think we are justified 

 in concluding that in the experiments made by Chauveau, the 

 virus, granting that it was properly selected, had not under- 

 gone that alteration during its transmission through the bodies 

 of the inoculated animals which modifies and mitigates its 

 virulence under ordinary circumstances, and that the virus 

 selected by Martin from a fatal case of small-pox was not 

 proper for an experiment where human life was at stake. 



Many experiments might be quoted (Ceely, Thiele, and 

 others) to prove that great uncertainty and difficulty often 

 attend the attempts to transfer the virus of variola from one 

 animal to another; that when variolous disease affects the 

 lower animals in a malignant form, it is capable of producing 

 by inoculation a disease of similar severity in man, and that 

 marked improvement sometimes takes place in the energy and 

 in the quality of the virus by subsequent removes or inocu- 

 lations in animals of the same kind, after the variolous viiais 

 had been successfully implanted in one of them ; it seems to 

 become less acrid, less virulent, and to acquire increased specific 

 activity; capable of inducing more pronounced and perfect 

 development of vesicles, with milder and less dangerous general 

 symptoms. 



Variola vaccinae has been transmitted back to the cow from 



