Pathogenicity. Natural Infection. 263 



are less susceptible (after a successful subcutaneous infection 

 they die in 6 to 7 days; showing enlarged spleen and necrotic 

 foci in the liver). Pigeons are only very slightly susceptible 

 (muscle necrosis develops after an intra-muscular infection), 

 while chickens are not susceptible. If the culture is injected 

 into the caecum of a rabbit, small white dots at first develop on 

 the mucous membrane (swollen lymph follicles) ; later ulcers 

 appear in sizes up to a lentil. 



By feeding large quantities of cultures or injecting cultures 

 into the intestines of hogs, either acute or more chronic inflam- 

 matory and necrotic processes develop, in some cases according 

 to the intensity of the infection (dysenteric necrosis and ulcera^ 

 tions on the intestinal mucous membrane, swelling and caseation 

 of the lymph glands, etc.). After previous starvation or neu- 

 tralization of the hydrochloric acid of the stomach, the disease 

 results in a much more acute and severe form, and the animal 

 may die on the third day with symptoms of septicemia (Salmon 

 & Smith). The subcutaneous injection of the culture results 

 in an inflammation of the neighboring lymph vessels and lymph 

 glands, leading to necrosis, and the animals die in from 2 to 3 

 weeks, or even later. In some of the cases ulcerations develop 

 in the meanwhile on the intestinal wall, and metastatic, caseous 

 areas appear in various internal organs. Intravenous injec- 

 .tions may result in a hemorrhagic septicemia producing death 

 in 1 to 3 days. The infection cannot be produced by inhalation. 



Contrary to the infection produced by virulent blood, hogs 

 which are infected with pure cultures of the bacillus suipestifer 

 do not transmit the disease to healthy hogs, and if they recover 

 they continue to be susceptible to natural infection. 



2. The bacillus suisepticus is in every particular identical 

 with the organism of pure swine plague (see p. 125). 



Natural infection results apparently from the digestive tract 

 and appears to be transmitted especially by the strongly viru- 

 lent urine of affected animals, while the excrements are fre- 

 quently only slightly or not at all virulent, and therefore play 

 a less important part in the transmission of the disease. In 

 piggeries of localities which were previously free of the disease 

 it always results from an introduction from the outside, while 

 in already infected premises and stables the affection may re- 

 peatedly appear without a new introduction, as the virus retains 

 its virulence for a long time outside of the animal body, in 

 fluids as well as in a dry material. This is proved by the fact 

 that the disease which was formerly unknown in Europe spread 

 in the course of the last decade along the road of swine traffic, 

 and then remained permanently in the infected countries, caus- 

 ing severe losses from year to year. 



The very extensive traffic in hogs which exists everywhere 

 and which is difficult to control, is generally the most effective 

 disseminator of the disease, and in this the hog markets, the 



