255 



due to the frequent presence of both huctciia in the surroundings of swiue, probii- 

 bly a result of frequent introduction. Either disease may be primary, according to 

 its relative virulence. 



(7) It is highly probable that the many attenuated varieties of either disease germ 

 can produce disease only when assisted by the other germ or by the unsanitary, 

 unphysiological methods of rearing swine, by which the latter arc reduced in 

 vitality and made more susceptible. 



(8) It is pretty well established that there are a number of infectious diseases 

 affecting cattle, buffaloes, deer, fowls, and smaller animals, the bacteria of which are 

 closely related if not identical with those of swine plague. These plagues appear 

 in various parts of the globe sporadically. ( Wild-und RiiuJerscuche, iarhone hitfaliuo, 

 fowl cholera, rabbit septicaemia.) Their tendency to sprciid from one species to 

 another, from cattle to swine for instance, probably depends on the degree of viru- 

 lence of the bacteria as well as the opportunities afforded for such transmission. 



(9) Swine-plague bacteria are very probably introduced into a herd only in the bodies 

 of animals, since they are speedily destroyed in soil and water by natural agencies. 

 Virulent varieties are perhaps always derived from preexisting disease. Attenuated 

 varieties may be introduced by healthy animals. Since these may under special 

 conditions giA'e rise to disease, efforts to prevent and suppress infection must take 

 into account the physical condition of the esj)osed animals. 



