PROPHYLAXY OF INFECTIOUS DISEASES. 
725 
produced by inoculation is often much less serious than the 
natural disease ; it lasts but a short time, can be given at the 
same time to all the animals exposed to contagion and which 
would become sick, little by little, one after the other, thus 
keeping up the disease in the invaded barn ; by this.method 
the duration of sanitary measures, always vexatious, trouble¬ 
some and expensive, is reduced. 
In the last century it was a common practice, especially in 
England, to inoculate small-pox to young folks. They had so 
many opportunities of contracting the disease that they con¬ 
sented to run the risk of the inoculation. A certain number 
would die, but much less than in a time of epidemic. 
This practice lasted until the days of Jenner, when he dis¬ 
covered vaccination and gave its inestimable practice to hu¬ 
manity. 
Direct variolization, however, still exists in some countries. 
In Algiers, for instance, the French have not yet succeeded in 
substituting vaccination for it. The Arabs remain attached to 
the traditions of their ancestors. With the fatalism of their 
belief they prefer to run the danger of the frequent accidents of 
variolization rather than adopt the practice of the Christians. 
Small-pox in sheep is a disease similar to human small-pox ; 
it resembles it so much that some authors call it improperly 
“swine variola.” It has fora long time been known that sheep 
recover from it, and will not again take it, and that by inocula¬ 
tion of its virus healthy animals can be protected. 
Clavelization is analogous to variolization ; like it, it gives 
the disease, but under a less serious form than natural conta¬ 
gion. 
Inoculation of the virus is done at the extremity of the ears 
or of. the tail; the disease develops in all the animals at the 
same time, and after five weeks, at the most, general health has 
returned. 
Clavelization has the objection of creating centres of conta¬ 
gion and of causing in some sensitive breeds a mortality which 
may go up from 2 to 10 per cent. It is for that reason that pre- 
