344 AGRICULTURAL BACTERIOLOGY. 



numbers. A rabbit is similarly killed in two days, and larger 

 animals in somewhat longer periods. Even a sheep may be 

 killed in two days by such an inoculation. The disease is 

 marked by a high fever and much discomfort and, after death, 

 the most characteristic symptom is a greatly swollen spleen, 

 whence the name splenic fever. The spleen is large, hard and 

 brittle, and contains enormous numbers of the bacilli. The 

 blood-vessels are also found to be full of them and the capil- 

 laries may be literally crammed with bacteria. The method 

 by which the bacillus produces its injurious effect upon the 

 body is not simply by the mechanical presence of the numerous 

 living parasites, but rather by the direct toxic action of certain 

 poisons which are produced by the bacteria. These toxic 

 bodies have been studied carefully, and may be regarded as the 

 direct cause of the disease and death of the animal, the bacteria 

 being the indirect cause. 



This bacillus is extremely virulent in its action upon suscep- 

 tible animals, so virulent, indeed, that a single bacillus, inocu- 

 lated under the skin of a susceptible animal, may be sufficient 

 to cause the disease and death. In the less susceptible ani- 

 mals it requires a larger dose to produce similar results. The 

 lesser susceptibility of such animals as the dog, the horse, the 

 bird, etc., renders them practically immune against spontane- 

 ous infection, and the disease only occurs in them as the result 

 of artificial experiment. In man the disease is of rare occur- 

 rence, being practically confined to people dealing in or 

 handling hides or wool, and is acquired by them either 

 through abrasions in the skin, when it produces malignant 

 pustule, or by breathing the spores into the lungs when it is 

 called the wool-sorters disease. 



The bacilli, however, vary greatly in their virulence. Some 

 cultures are extremely potent, as just mentioned, while others 

 an far less so; and some, indeed, so weak in their action 

 as to be unable to produce a fatal disease even in susceptible 



