498 SMALLPOX AND VACCINATION. 



also had this effect. This inoculation method had long 

 been practised in various parts of the world, and had con- 

 siderable 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 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 subsequently 

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

 disease was thus identical with horsepox in epidemics of 

 which it had its origin. Jenner was, however, probably in 

 error in confounding horsepox with another disease of 

 horses, namely grease. Cowpox 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 small- 

 pox, 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 Vaccituz. Though from the first Jennerian 

 vaccination had many opponents, it gradually gained the 

 confidence of the unprejudiced, and became extensively 



