FOWL CHOLERA. 
339 * 
the limpid liquid which it contains to become opalescent, or tur¬ 
bid, within twenty-four hours, and a microscopic examination 
shows this turbidity to be due to vast numbers of the dumb-bell 
forms already mentioned. If the blood is obtained and intro¬ 
duced with proper care, it will be in vain for us to search our 
preparations for other forms of bacteria, and no matter how long 
we preserve our cultivations, or at what temperature we keep 
them, the result will be the same. Having made a pure cultiva¬ 
tion of the organism, if our apparatus is perfect it will remain 
pure indefinitely. 
With a single cultivation and without other tests, we might 
be uncertain whether the bacterium obtained really existed in the 
blood, or whether it was of atmospheric origin; but when we 
have repeated the experiment a considerable number of times, 
always obtaining organisms morphologically the same, and these 
very different in essential characteristics from the bacteria which 
multiply in similar liquids after exposure to the air, we are war¬ 
ranted in concluding that they were not introduced from the air 
but from the blood. 
Now, when we have proved that a certain bacterium exists 
during life in the blood of affected birds, is that good evidence 
that the disease is caused by such organisms ? Evidently, it is 
very insufficient, but fortunately we are able to satisfy the most 
fastidious on this point, by additional facts. 
2. Liquids in which bacteria are cultivated produce the disease 
by inoculation. If we add one-fourth of a drop of virulent blood 
to five hundred drops of cultivation-liquid, and place this in an 
incubator at 90 deg. Fahr. for twenty-four hours, or until the 
development of micrococci has produced turbidity, we find that 
inoculation with this liquid as surely produces the disease, and 
that this is as fatal as when virulent blood is the material used. 
But there is a point here that is nearly always overlooked by 
those who make this class of investigations : perhaps this cultiva¬ 
tion, as we call it, is only a dilution of the original virus—a dilu¬ 
tion not sufficient to destroy its activity. We have used a half¬ 
ounce or more of liquid, and have made a dilution of 1 to 2000— 
a dilution much greater, it is true, than is usually made by those 
