THE CAUSE OF CHOLERA 87 



animals, but also to the final eradication of hog-cholera from 

 American soil, as has been done in the case of foot-and-mouth 

 disease and contagious pleuropneumonia. 



THE CAUSE OF CHOLERA 



As is the case with many diseases present in man, hog-cholera 

 has long been believed to be due to some sort of germ infection. 

 The discovery of germs and their relation to disease was made only 

 within the past fifty years, and ever since this germ relationship 

 to disease has been proved, veterinary surgeons in this country and 

 in Europe have been trying to discover some germ which could be 

 definitely set down to be the cause of hog-cholera. 



Hog-cholera Bacillus. — About 1885 the officials of the United 

 States Bureau of Animal Industry discovered and described a germ 

 which was called the bacillus of hog-cholera, and which was for 

 many years believed to be the active cause of hog-cholera. 



This germ was very small — only about five-one-hundred-thou- 

 sandths of an inch in length — shaped like a rod, and with rounded 

 ends. The hog-cholera bacillus is very active, and when looked at 

 on a glass shde under the microscope is found to possess a number 

 of hair-like legs called flagella, by means of which it has the power 

 of very rapid movement. In the laboratories of our state colleges 

 and in every laboratory where studies of germs are made this germ 

 can be easily grown on the various forms of culture-media or germ 

 foods which are there used for that purpose. It grows best in 

 foods that contain a small amount of salt, and shows its most rapid 

 growth when these foods are kept at about the temperature of the 

 animal body. In these laboratories special germ-growing incu- 

 bators are provided for this purpose. It will grow either in the 

 presence or absence of air. The germs multiply by simple division 

 or fission. In these laboratories many stains are used by which 

 the germs can be stained when mounted on glass slides and very 

 beautifully demonstrated under the microscope, which is a power- 

 ful magnifying instrument used for the purpose of examining germs. 



Not True Cause of Cholera. — In the blood and in the ulcerated 

 bowels of an animal that has died of hog-cholera the hog-cholera 

 bacilli are found in very large numbers, but in the past few years 

 we have come to doubt that this germ is the cause of cholera, be- 



