EXPERIMENTAL ANTHRAX. 305 



It is important to note the existence of great differences 

 in susceptibility to anthrax in different species of animals. 

 Thus the ox, sheep (except those of Algeria, which only 

 succumb to enormous doses of the bacilli), guinea-pig, and 

 mouse are all very susceptible, the rabbit slightly less so. 

 The last three are of course most used for experimental 

 inoculation. We have no data to determine whether the 

 disease occurs among these in the wild state. Less sus- 

 ceptible than this group are the horse, deer, goat, in which 

 the disease occurs from time to time in nature, as it also 

 does, though rarely, in the pig. The human subject may 

 be placed next in order of susceptibility, man thus occupy- 

 ing a medium position between the highly susceptible 'and 

 the relatively immune animals. The white rat is highly 

 immune to the disease, while the brown rat is susceptible. 

 Adult carnivora are also very immune, and the birds and 

 amphibia are in the same position. 



With these differences in susceptibility there are also 

 great variations in the pathological effects produced in the 

 natural or artificial disease. This is especially the case 

 when we consider the distribution of the bacilli in the 

 bodies of the less susceptible animals. Instead of the 

 widespread occurrence described above, they may be con- 

 fined to the point where they first gained access to the 

 body and the lymphatic system in relation to it, or may be 

 only very sparsely scattered in organs such as the spleen 

 (which is often not enlarged), the lungs, or kidneys. Never- 

 theless the cellular structure of the organs even in such a 

 case may show changes, a fact which is important when we 

 consider the essential pathology of the disease. 



Experimental Inoculation. Of the animals commonly 

 used in laboratory work, white mice and guinea-pigs are the 

 most susceptible to anthrax, and are generally used for 

 test inoculations. If a small quantity of anthrax bacilli 

 be injected into the subcutaneous tissue of a guinea-pig, a 

 fatal result follows, usually within two days. Post mortem 

 around the site of inoculation the tissues, owing to intense 

 inflammatory oedema, are swollen and gelatinous in appear- 

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