PREDISPOSING CAUSES 103 



for cholera. The localized outbreaks of cholera that do occur dur- 

 ing the winter months are very often due to lowered resistance on 

 the part of the animals, due to the poor sanitary surroundings in 

 which they are kept. 



While no specific germ for hog-cholera has ever been definitely 

 demonstrated, yet we are firm in the belief that such an organism 

 does exist, and from what we know of other germs we are able to 

 determine further reasons why outbreaks of cholera are less numer- 

 ous in the winter season. Practically all germs are rendered inert 

 and incapable of reproduction by cold, and especially by freezing. 

 Many of them are entirely destroyed by prolonged exposure to 

 cold. That this is true in the case of the hog-cholera virus would 

 seem to be beyond doubt, and is unquestionably one of the im- 

 portant reasons why cholera is less common in the winter season. 



In this connection, it might also be stated that repeated obser- 

 vations seem to bear out the idea that after a severe winter hog 

 lots are frequently freed from cholera which had been infected 

 during the previous season. 



Another common factor in starting an outbreak of hog-cholera 

 is the unearthing of bones and parts of carcasses of buried animals 

 by dogs and other animals during the summer season. In the win- 

 ter months, after the ground is frozen, this source of danger is 

 removed. 



There are, then, we find, many very good reasons why the out- 

 breaks of hog-cholera are more numerous and more severe and wide- 

 spread during the summer and early fall months. We must re- 

 member, however, that the disease may occur equally severe in 

 winter, and in winter epidemics the danger from lung compHcations 

 is, of course, more marked than during the summer months. 



(6) Geographic Location. — This, a few years ago, might have 

 been considered a factor in determining an outbreak of cholera, 

 but at the present time cholera is so widespread throughout the 

 herds in the United States that all parts of our country may be said 

 to be equally well inoculated with the disease. 



In practically every state where hogs are raised this disease 

 has repeatedly ravaged the herds, and so widespread has become 

 the scattering of these epidemics that no one state can hardly be 

 regarded as a more pronounced cholera-infected district than 



