FAKMEKS' INSTITUTES. 775 



like the swiue plague bacillus have been fouud iu the lungs of other ani- 

 mals. If upon further investigation they should be fouud to be the same, 

 it will add to our knowledge of the nature of the affection and make us 

 less ready to claim tliat the disease can be eradicated by sanitary meas- 

 ures. 



The Way by Which the Germs Enter the Body.— Experiments have 

 been conducted to determine how the germs find their way into the body 

 to cause disease. Hogs fed upon the carcasses of animals affected v^ith 

 cholera develop a virulent form of the disease in a short time. The in- 

 testines become the seat of typical lesions, while other parts are not se- 

 riously affected. If the germs be placed upon food or in drinking water 

 they will produce a like result. These experiments show that if the 

 germs be ingested with the food or water they will develop and produce 

 the disease. 



The germs have been sprayed in the air and hogs made to inhale 

 them, also injected into the windpipe, but the disease did not develop, 

 which may be taken to indicate that in nature the disease germs do not 

 find a point for development in the lungs, or at any rate not as a primai-y 

 focus. 



The germs have been inoculated beneath the skin, but it is only 

 when very large numbers are used that disease occurs. This would 

 seem to indicate that the hog does not contract the disease from inocula- 

 tion, as by tlie bite of the louse and injuries. 



A similar line of experiments conducted with swine plague shows 

 that it does not cause trouble when swallowed, but does do so easily 

 when made to inhale air containing the germs or when germs are in- 

 jected into the windpipe. The lungs are the primary seat of the affection, 

 and thus differs from hog cholera. Inoculation experiments, l)oth sub- 

 cutaneous and intravenous, require such large numbers of germs that 

 it would seem that natural inoculation by the louse bite could hardly 

 prove fatal. 



The conclusions from these experiments are that in nature cholera Is 

 caused by the ingestion of the germs with the food or water, and swine 

 plague by inhalation. 



Accessory Causes.— We consider all those factors which lower the 

 resistance of the animal or which disseminate or pi'opagate the germs 

 as being accessory causes. 



Among the causes which tend to lower the resistance we mav con- 

 sider feeding, shelter and breeding. The disease is often attril)uted to 

 tiie feeding of green corn, too much corn. etc. In 1S9G tlie Iowa Weather 

 Bureau published a maj) showing the distribution of the disease in the 

 State. It was found that the greatest losses were sustained in those 

 counties where corn constituted an almost exclusive diet. The lowest 

 death rate was sustained In those counties in which dairying was an 

 important industry and milk was largely used as a feed. Tliis was 



