INFECTIOUS DISEASES 1 37 



as a distinct disease, occurred. This controversy 

 occupies a prominent place in the history of the 

 disease. 



Causes. — The specific cause is the bacillus of 

 swine plague, a small rod or oval shaped germ. 

 When taken from the diseased tissues, it is about 

 .00004 of an inch in length and .000024 oi an inch 

 in breadth, but in the laboratory when cultivated 

 on the different kinds of media and under differ- 

 ent conditions, its appearance varies and it may 

 grow to twice the above' dimensions. ; 



The germ is non-motile and does not .grow 

 readily, or not at all, on some of the common 

 nutrient medias, such as potato and gelatine. It 

 grows in the presence of oxygen and cultures pos- 

 sess a disagreeable odor. It is not as hardy as 

 the hog cholera germ, and if the conditions are not 

 favorable for its growth, it soon dies. It is readily 

 destroyed by drying and disinfectants. 



Accessory Causes. — Attenuated or weakened 

 varieties of the swine plague germ are frequently 

 found in the air passages of healthy hogs. For 

 this reason, the germ is widely distributed, but 

 unless the animal is debilitated, or the activity of 

 the germ increased in some way, it does not pro- 

 duce disease. A frequent method of infection 

 occurs through susceptible animals coming in con- 

 tact with swine having a mild form of the disease. 

 Isolated cases of swine ■ plague are more or less 

 common, but there is always danger of its spread- 

 ing rapidly under favorable conditions. Its dis- 



