ANTHRAX OR SPLENIC FEVER 303 
really demonstrated as the cause of the disease until 1875, by the 
work of Koch, and shortly afterward by Pasteur (Fig. 51). After 
some twenty-four years of dispute the final demonstration was 
due to 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 
Fic. 51.-~B. anthracis, the cause of splenic fever. 
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 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 con- 
tinuing 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 
