CHICKEN CHOLERA. 
133 
another twenty with the weakest virus I can obtain, and none die. 
Are the animals thus vaccinated safe from the effect of the more 
active virus ? Yes; but only a certain proportion of their num¬ 
ber. Indeed, if I inoculate them with strong virus, six or eight 
for instance, though sick, will not die, a fact to be weighed in con¬ 
nection with the effect of the first twenty vaccinations, which all 
resulted in death. From the first lot, I then take twenty fresh 
hens and inoculate them twice, at intervals of seven or eight days. 
Are they now protected against infection by the stronger virus \ 
To obtain an answer, let us proceed to inoculate with it. This 
time, the result will vary from that of the second experiment; 
it will not be six or eight which will survive, but twelve or 
fifteen. Again, if I take from the first lot of fresh hens twenty 
others, and vaccinate them successively with attenuated virus, 
not once alone, but three or four times, the mortality which would 
have followed the inoculation with very strong virus, (the disease 
itself), will cease. In this case, it is evident that the animals 
have been brought to the condition of those which never con¬ 
tract the disease. 
A plausible explanation of the non-recidivity referred to may be 
found in the theory that the microbe (the cause of the disease) 
finds, in the body of the animal, a congenial medium of culture, 
and to satisfy the requirements of its own existence, alters or de¬ 
stroys (which, in the present case, are equivalent terms) the 
elements of its own nutrition, which it either elaborates and ap¬ 
propriates to its own growth, or consumes with the oxygen which 
it borrows from the blood of the fowl. 
When complete immunity is obtained, one may inoculate any 
of the muscles with the most virulent microbes without producing 
the slightest effect. In other words, the culture has become im¬ 
possible in these muscles, inasmuch as they no longer contain the 
proper food of the microbe. 
One cannot express his impressions when observing these 
phenomena. Here are twenty hens which have never been 
affected with the disease. I inoculate them in the thigh with the 
most effective virus, and carefully observe the effects of the inocu¬ 
lation. The next day all are down, very lame, very sleepy ; the 
