458 SMALLPOX AND VACCINATION. 



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 dis- 

 covery 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, or 

 grease, especially tending to occur in wet cold springs, 

 which consists in an inflammatory condition about the 

 hocks, giving rise to ulceration. Jenner believed that the 

 matter from these ulcers, when transferred by the hands of 

 men who dressed the sores to the teats of cows subse- 

 quently milked by them, gave rise to cowpox in the latter. 

 This disease was thus in reality identical with horsepox, 

 in epidemics of which it had its origin. In the cow, it 

 manifests itself as a papular eruption on the teats. The 

 papules become pustules; their contents dry up to form 

 scabs, or more or less deep ulcers are formed at their 

 sites. From such a lesion the hands of the milkers may 

 become affected through abrasions, and a similar local 

 eruption occurs, with general symptoms in the form of slight 

 fever, malaise, and loss of appetite. It is this illness which, 

 according to Jenner, gives rise to immunity from smallpox 

 infection. He showed experimentally that persons who had 

 suffered from such attacks did not react to inoculation with 

 smallpox, and further, that persons to whom he communicated 

 cowpox artificially, were similarly immune. The results of 

 Jenner's observations and experiments were published in 

 1798 under the title An Inquiry into the Causes and Effects 

 of the Variola Vaccince. Though from the first Jennerian 

 vaccination had many opponents, it gradually gained the 

 confidence of the unprejudiced, and became extensively 

 practised all over the world, as it is at the present day. 

 The evidence in favour of vaccination is very strong. 



