184 THE FARMER'S VETERINARIAN 



poison may be very easily demonstrated. The 

 curious relations to this disease of the old bacilli 

 of hog cholera and of swine plague are not well 

 understood, but it seems quite possible that they 

 may play some part in the later development of 

 the disease after the disease processes have been 

 started by the invisible germ. While our old 

 theories and supposed information concerning the 

 cause of hog cholera have been very much dis- 

 turbed by newer work, it is important to remember 

 that hog cholera is now just as much as before to 

 be recognized as a distinctly infectious disease. It 

 is important to remember also that this infection 

 is absolutely necessary, or there can be no cholera 

 no matter how susceptible animals may be. 

 There can be no cholera without this primary and 

 specific cause any more than there can be plants 

 in our wheat fields without the previous presence 

 of mustard seed. Conditions of soil and climate 

 may favor a rank growth of mustard. Conditions 

 of feed and keep may favor the development and 

 spread of hog cholera. They may decrease resist- 

 ance and increase susceptibility, but cannot origi- 

 nally cause the disease. It is a rather common ex- 

 perience that hogs kept closely housed and fed, 

 especially with such foods as corn, offer less resist- 

 ance than do other hogs. In our vaccine work we 

 frequently find hogs of this type which die readily 

 under inoculation with blood of low grade virulence. 

 Hogs of hardier type may become slightly sick or 

 not sick at all with inoculation from the same in- 

 fectious material. Pampered show herds appear 

 especially susceptible to both natural infection and 

 artificial inoculation. 



The farmer, and for that matter the public in 

 general, should bear in mind that the cause of hog 



