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 

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