ANTHRAX OR SPLENIC FEVER. 281 
such experiments as the following. It was easy to show by the 
microscope that this organism is present in the blood of the animals 
suffering from the disease, and that a drop of such blood, containing 
the organism, when injected into healthy animals would inevitably 
produce the disease in the inoculated animals. But this did not 
necessarily prove their causal agency, for it was possible to claim 
that there were some other poisons in such blood. For final proof 
it was necessary to separate the bacteria from the drop of blood, 
cultivate them, and inoculate animals with the pure cultures. At 
the time that this disease was first being studied no methods were 
known of obtaining isolated bacteria in pure cultures, and hence 
FIG. 52. B. anthracis, the cause of splenic fever. 
the long dispute. Pasteur finally procured his results as follows. 
Finding that the bacterium would grow in a solution made by steeping 
yeast in water, Pasteur inoculated a sterile flask of such yeast-water 
with a drop of anthrax blood. In a day or two his flask was filled 
with bacteria which had arisen from the first by division. The 
inoculation of a second flask from the first showed like results, and 
by continuing such inoculations from flask to flask he rapidly got 
rid of all parts of the original drop of blood, except such parts as had 
been multiplying in the flasks. His microscope showed him that the 
only thing that multiplied and remained in his later flasks were the 
bacteria present in the original drop of blood. Nevertheless, he 
found that though he continued these inoculations indefinitely, 
every flask was equally virulent, and a small drop of the culture 
would inevitably produce anthrax in a susceptible animal in a very 
few hours, the development of the disease being always accompanied 
by the growth in its blood of the bacilli in countless myriads. These 
24 
