PROPHYLAXY OF INFECTIOUS DISEASES. 
731 
to the interest of every one to apply it for himself, and in this 
way the great losses due to this disease, which are constantly 
increasing, will be suppressed. 
Pasteurian vaccination has then rendered unappreciable ser¬ 
vice to agriculture in every country ; the vaccination of ani¬ 
mals is counted by hundreds of thousands throughout the entire 
world. Yet it cannot be applied in all cases ; to give the full 
effect it must be done as a preventive—that is, to animals which 
have not yet resisted the germ of the disease ; they do not grant 
immunity except after a certain length of time—which is never 
less than 20 days—necessary for immunization. 
Already noticeable in braxy in sheep, the requirement be¬ 
comes still more serious in cases of rouget, whose march is so 
rapid and its effects so serious. If we wait for the disease to 
appear it is too late, as during the 20 days required to obtain 
immunization all the animals will have died. We will see di¬ 
rectly how to remedy this by resorting to serotherapy. 
(3) PROPHYLAXY BY SEROTHERAPY. 
This is not the place, nor is there time to explain to you the 
scientific principles of serotherapy. What is important for you 
to know is that for many infectious diseases the blood of im¬ 
munized animals, those which have been vaccinated and satu¬ 
rated with virus, contains substances which are able to destroy 
the virus or prevent its development, or neutralize the effect of 
the toxines that it secretes, in such a manner that if the serum 
is injected under the skin of a healthy animal, it is vaccinated 
against the inoculation of the virus in doses which are always 
fatal to the witnesses. You all know the marvelous results ob¬ 
tained by this method in the treatment of diphtheria. The 
important thing is to know that the serum of an immunized 
animal can act as a vaccine ; it acts quicker than attenuated . 
virus, and its action does not last so long. It can be introduced 
even after the virus has entered the organism and sometimes 
after the first manifestations of the disease and still act; when 
from 5 to 10 cubic centimetres are injected under the skin, a 
little swelling is observed, which in a few minutes, as the serum 
