538 SWINE IN AMERICA 



the disease. Anything which tends to lower the health 

 of the animals may be regarded as a predisposing cause. 

 Among such predisposing factors are improper feeding, 

 an insanitary condition of the hog lots, damp or cold 

 sleeping places, and dirty drinking and feeding troughs. 

 Insanitary surroundings and poor feed can not in them- 

 selves produce cholera, but they lower the vitality of 

 hogs to such an extent that they become comparatively 

 easy victims of any disease-producing germs to which 

 they are exposed. 



WAYS IN WHICH THE CHOLERA GERMS REACH A HERD 



"Although the conditions just mentioned undoubtedly 

 exert considerable influence upon the relative resisting 

 powers of hogs to cholera, the disease can be started in 

 a herd only by introducing the germ which causes it. 

 This germ is always present in the bodies of sick hogs, 

 and is thrown off from them in large numbers in the 

 feces and urine, thus contaminating the yards or pens 

 in which sick hogs are kept. The most dangerous factor 

 in spreading cholera is, therefore, the sick hog; but any 

 agency which might serve to carry a particle of dirt 

 from infected yards may be the means of starting an 

 outbreak. 



"Sick hogs may get onto a farm (i) by escaping 

 from a neighboring herd, (2) by the purchase of new 

 stock which may show no symptoms of sickness until 

 some days after purchase, (3) by returning show hogs 

 to the herd after visits to fairs or stock shows, (4) by 

 purchase of hogs which have apparently recovered from 

 cholera. The risk incurred by purchase of new hogs or 



