282 BACILLI OF THE TYPHOID GROUP 



hogs, and also that the disease lacks several of the essential features 

 of acute hog cholera. 



The experiments with blood serum derived from hogs sick of hog 

 cholera and proved to be free from Bacillus cholerse suis show, on 

 the contrary, that such serum, upon subcutaneous injection, produces 

 illness in hogs with great regularity, and, furthermore, that the disease 

 thus produced possesses all the characteristics of the natural disease 

 including symptoms, lesions, contagiousness, infectiousness of the 

 blood, and immunity in those animals which recover. The striking 

 contrast of these results with those obtained when cultures of the 

 Bacillus cholerse suis are used and their complete agreement with 

 the results obtained from unfiltered blood of sick hogs make the 

 conclusion necessary that some virus other than Bacillus cholerse suis 

 exists in the blood of hogs suffering from acute hog cholera, and that 

 this virus is necessary for the production of the disease. 



This virus is only known by the effects it produces. Every attempt 

 to discover by microscopic examination or by the usual cultural 

 methods a visible microorganism in these filtrates has failed com- 

 pletely. There can be no doubt that the pathogenic power of the 

 filtered blood is due to some living agent endowed with the power of 

 reproduction and not to the presence of a toxin alone, because the 

 disease induced by the filtered serum is communicated from sick to 

 healthy animals by association, and, moreover, because the disease 

 induced by filtered serum has been transferred to a second and even 

 a third animal by subcutaneous injections, the serum being filtered 

 each time previous to inoculation. 



While experiments by Dorsett, Bolton, and McBryde established 

 beyond question that the filterable virus was present in all the out- 

 breaks of hog cholera studied experimentally by these authors, it is 

 also true that the Bacillus cholerse suis was present almost as uni- 

 formly. Even were the investigators named so inclined, it would, for 

 this reason, be impossible to overlook the part which this organism 

 may have played. From the results of inoculations with the filterable 

 virus, however, and those obtained with cultures, one is compelled 

 to conclude that the prime cause in these cases was the filterable 

 virus, and that the Bacillus cholerse suis was at most an accessory 

 factor. 



The exact role of the Bacillus cholerse suis in outbreaks of acute 

 hog cholera is difficult to define. That the fatal result in many 

 instances is materially influenced by the presence of that organism can- 

 not be doubted; in addition, the fact should be emphasized that 

 although the filterable virus appears to have been the primary invader 

 in the cases of acute hog cholera investigated, the possibility of 

 independent disease being caused by Bacillus cholerse suis cannot be 

 denied. In fact, belief in such a possiblity is difficult to avoid when 

 the very considerable pathogenic power for hogs exhibited by many 

 cultures of that organism when fed or administered intravenously is 

 considered. 



