146 HOUSEHOLD BACTERIOLOGY 



of it. But, just the same, he led the way to the prac- 

 tical banishment through artificial immunity of one of 

 the greatest and most dreaded scourges of man. 



It was known in Jenner's time that those who 

 milked cows having sores upon the udder, due to a 

 local affection called cowpox, often acquired similar 

 sores upon their hands. These soon healed, involving 

 only a slight illness. But such persons had become 

 partially or wholly immune to the more serious disease 

 of man, smallpox. 



Jenner studied this subject carefully and came to 

 the conclusion that artificial inoculation with a very 

 small portion of material taken from such cattle might 

 be practiced on a large scale with beneficent results. 

 In spite of much opposition he urged his views, which 

 were gradually accepted, until at last the method has 

 become almost universal in civilized communities. 



Large and carefully managed establishments are 

 now devoted to the preparation of the virus, as it is 

 called, by which artificial immunity to smallpox is se- 

 cured. The slight affection of animals calves from 

 which the virus is taken. is called vaccinia, while the 

 disease corresponding to it in man, smallpox, is called 

 variola. 



The method now practiced on the large scale is very 

 simple. Healthy calves are carefully cleansed and kept 

 in clean, airy stalls. The belly is shaved and most 

 scrupulously freed from all possible sources of con- 

 tamination. Into this clean surface, slightly scarified, 



