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. 
