APPENDIX A. 



SMALLPOX AND VACCINATION. 



Smaixpox is a disease to which much study has been devoted 

 owing, on the one hand, to the havoc which it formerly wrought 

 in Europe, — a havoc which at the present day it is difficult to 

 realise, — and, on the other hand, to the controversies which 

 have arisen in connection with the active immunisation against 

 it introduced by Jenner. Though there is little doubt that a 

 contagium vivwin exists, the etiological relationship of any par- 

 ticular organism to smallpox has still to be proved ; and with 

 regard to Jennerian vaccination, it is only the advance of 

 bacteriological knowledge which enables us to understand the 

 principles which underlie the treatment, and which furnishes 

 methods whereby the vexed questions concerned may be satis- 

 factorily settled. 



Jennerian Vaccination. — Up to Jenner's time the only 

 means adopted to mitigate the disease had been by inoculation 

 (by scarification) of virus taken from a smallpox pustule, 

 especially from a mild case. By this means a mild form of the 

 disease was often originated. It had previously been known 

 that one attack of the disease protected against future infection, 

 and that the mild attack produced by inoculation also had this 

 effect. This inoculation method had long been practised in 

 various' parts of the world, and had considerable popularity all 

 over Europe during the eighteenth century. Its disadvantage 

 was that the resulting disease, though mild, was still infectious, 

 and thus might be the starting-point of a virulent form among 

 unprotected persons. Jenner's discovery was published when 

 inoculation was still considerably practised. It was founded on 

 the popular belief that those who had contracted cowpox from 

 an affected animal were insusceptible to subsequent infection 

 from smallpox. In the horse there occurs a disease known as 

 horsepox, especially tending to arise in wet, cold springs, which 

 consists in an inflammatory condition about the hocks, giving 



