PROPHYLAXY OF INFECTIOUS DISEASES 
727 
experimental medicine was in its infancy, Willems demonstra¬ 
ted the benefit that could be derived from inoculation against 
contagious pleuro-pneumonia. He proved that the disease 
could be inoculated, and that when it was in the peripheric re¬ 
gions, the ear or the tail, the lesion produced was ordinarily 
mild ; finally, he demonstrated that after recovery the animal 
was refractory to the natural disease. This great discovery has 
had the fate common to many others, and it was specially in 
Belgium that it was contradicted. 
Numerous experiments made in every country upon large 
numbers of animals have proved the entire efficacy of the 
method ; the inoculation of Willems applied as a preventive 
upon animals free from the germ of the disease, protects them 
absolutely against the natural infection. This inoculation has 
found its way into the French Sanitary Commission, which 
orders it upon all animals in an infected commission stable. 
Unfortunately, in an infected stable there are many animals 
that have the germ of the disease ; for this reason inoculation 
cannot always give good results : to give all that it can do, it 
• * 
must be applied as a preventive. 
To inoculate as a preventive the virus of rinderpest, an¬ 
thrax, rouget of swine, Texas fever, or horse sickness must not 
be thought of; it would give as serious a disease as the natural 
one and kill most of the inoculated. 
* ^ * 
The discovery of vaccine is the fact of a lucky hazard, but 
a luck which happens only to those who are worthy, those who 
know how to see and understand the meaning of what they see. 
The service it has rendered cannot be appreciated, and it is but 
justice to consider Jenner as one of the greatest benefactors of 
humanity. But the discovery of Jenner remained an isolated 
fact. It belonged to another genius, our great and immortal 
Pasteur, to generalize the principle of vaccination, to immunize 
at will against diseases much more serious than small-pox 
itself. 
To take a virus whose inoculation is fatal, cultivate it arti- 
