go SWINE PLAGUE 



form virulence for years is well exemplified by a variety iso- 

 lated in the summer of 1890. This variety was fatal to 

 rabbits within twenty hours when first isolated and this 

 degree of virulence maintained itself for a period of nearly 

 four years. 



§ 76. Modifications of the septicemic type by in- 

 creasing the resistance of rabbits. By the injection of steril- 

 ized cultures which increase the resistance of rabbits, Smith 

 and Moore were able to produce nearly all the pathological 

 variations which follow the inoculation of natural races of 

 swine-plague bacteria as isolated from outbreaks. This modi- 

 fication of the septicemic type is not fortuitous, for among the 

 large number of rabbits inoculated during three and one- 

 half years with the culture employed, none survived 

 twenty to twenty-four hours. Whenever the course of the 

 inoculation disease in rabbits departed from this rapidly fatal 

 type, it was due to some preliminary treatment of the rabbit. 



The degree of resistance determined quite regularly 

 though not invariably the form of the disease. This degree 

 was measured by the relative quantity of the protective ma- 

 terial (sterilized cultures, sterilized blood, and blood serum) 

 injected. The grades of disease induced range themselves in 

 the following order : 



'& 



1. No resistance — acute septicemia. 



2. Slight resistance — peritonitis. 



3. Increased resistance — pleuritis and pericarditis with or with 



out secondary pneumonia. 



4. Higher degree of resistance— pleuritis and peritonitis. 



5. Still greater resistance — irregular lesions in the form of ab- 



scesses, subcutaneous and subperitoneal. 



6. Nearly complete immunity. Very slight reaction at the 



point of inoculation. 



Most of the cases cited below as illustrating these modified 

 forms of the septicemic type belong to the series of immuniz- 

 ing experiments of the preceding article. To this the reader 

 is referred for additional illustrations. 



