BUREAU OF ANIMAL INDUSTRY. 655 



It is our intention to continue experiments which may throw more 

 light upon this mode of infection. 



Perhaps the most common source of infection is the food and drink. 

 That is, the virus enters the alimentary canal, and there produces 

 such extensive ulceration that the animal sooner or later succumbs 

 from gradual exhaustion, septic poisoning, or peritonitis. Or the 

 virus immediately enters the blood from the intestines, multiplies in 

 every organ of the body, and causes death in a few days, or even 

 hours. Such sudden deaths usually occur at the beginning of severe 

 epidemics. Pigs which are fed with the internal organs of those that 

 have died of the disease almost invariably take the disease in a very 

 severe form, and die within one or two weeks after infection. To 

 demonstrate that it was the specific bacterium of hog-cholera in 

 these internal organs, and not some other element, pigs were fed with 

 liquids which contained only this organism, and they produced the 

 most severe disease. These demonstrations, together with the com- 

 monly observed fact that the disease seems to exist in the large intes- 

 tine only, prove conclusively that the virus is introduced largely with 

 food and drink. 



It has already been stated that the most common seat of the disease 

 is the large intestine. The food after leaving the stomach passes in 

 a liquid condition through the small intestine, so that this never seems 

 filled; in fact, its only contents are a coating of semi-liquid matter 

 over the mucous membrane. It passes through the small intestine 

 quite rapidly, but on i»eaching the large intestine the undigested re- 

 mains become more consistent, because the liquid is reabsorbed, and 

 are kept here for some time. The bacteria, if not destroyed by the 

 gastric juice, pass quickly through the small intestine, but in the 

 large intestine they begin to multiply and attack the mucous mem- 

 brane, which they destroy. Hence the feces or discharges of diseased 

 pigs, wherever deposited, scatter larger or smaller quantities of the 

 virus, which may induce the disease over and over again. The dis- 

 charges, then, must be looked upon as the chief vehicle for the virus 

 when the disease has taken hold of a herd. Pigs endowed with the 

 "well-knov/n habits will not hesitate to avail themselves of the oppor- 

 tunity of becoming infected whenever it is offered, But the dis- 

 charges are not the only moans by which the virus is disseminated 

 and kept alive. We have shown that the bacterium constituting the 

 living virus is a very hardy germ, and one endowed with great pow- 

 ers of multiplication. In the laboratory it has grown luxuriantly in 

 milk and on boiled potato. It grows slightly in hay infusion, even 

 in urine not neutralized. The temperature throughout the summer 

 in most of the States is sufficiently elevated to permit the growth of 

 the bacterium in these various substances, since a temperature of 70° 

 F. is amply sufficient, and temperatures above this point simply favor 

 the rate of increase of the quantity of virus. Even in good drinking 

 water the virus will increase for four or five days and remain alive 

 for months. 



There is consequently very little about a pen in which the virus, 

 when scattered in the discharges of infected animals, will not in- 

 crease in quantity and form a more potent source of infection. It 

 will multiply in the wet soil, iii the drinking water, and in the semi- 

 liquid food A gallon of milk inoculated with a minute portion of 

 infectious material and allowed to stand through a warm night in 

 midsummer might be sufficient to produce the disease in at least a 

 dozen animals if fed to them on an empty stomach. 



