252 HOG CHOLERA 



characteristic of hog cholera have been produced (Welch). By feeding 

 pigs with pure bouillon cultures the intestinal lesions typical of hog 

 cholera have also been obtained (Smith). 



Rabbits inoculated subcutaneously with o. i c. c, of a bouillon cul- 

 ture die in from 5 to 8 days. The essential lesions consist of necrotic 

 foci in the liver and a very much enlarged and dark colored spleen. 

 Guinea pigs are affected similarly to rabbits, but death does not usually 

 occur until from 7 to 12 days. Pure cultures of the bacillus can be 

 obtained from the blood, liver or spleen of the inoculated animals. 



While the above description applies to the form most 

 frequently encountered, varieties are not uncommon. In 1894 

 Smith called attention to several varieties of this species. It 

 is interesting to add, that Reed and Carroll have found the 

 bacillus isolated by Sanarelli, and thought by him to be the 

 cause of yellow fever, to belong to this group of bacteria. 



In 1903, de Schweinitz and Dorset published the discovery 

 of a disease practically identical in its manifestations with hog 

 cholera of an acute type, but which was produced by a virus 

 that passed through the finest porcelain filters. It is possible, 

 therefore, that the disease now known as hog cholera may be 

 differentiated into two maladies, one caused by B. cJiolerae siiis 

 and the other by the "invisible virus." McClintock, Boxmeyer 

 and Siffer report like results in the production of a disease with 

 the filtrate. These authors were unable to find the hog-cholera 

 bacillus in the cases from w^hich they obtained the invisible 

 virus. This suggests that they are dealing with a new disease 

 rather than with a new etiological factor for hog cholera. 

 Until this infectious filtrate is obtained from animals from 

 which pure cultures of B . cholerae suis were isolated from the 

 organs, it seems unfortunate to consider it the cause of hog 

 cholera. The experimental results obtained \\\\.\x B . cholerae stiis 

 are too convincing to relegate it, without sufficient evidence, to 

 the role of a secondary invader. 



More recently Dorset, Bolton and McBryde have con- 

 firmed the earlier publication by de Schweinitz relative to the 

 filterable virus. Thej' state, however, that " it must be ad- 

 mitted that a disease in hogs may exist which is due to 

 B. cholerae suis, and which has no connection with the filterable 



