INFECTIOUS DISEASES 173 



chseta suis, as well as the Berkefeld filtrates of the same transfers, are 

 capable of producing hog cholera and marked reactions, which confer 

 more or less protection against the disease. The pathogenicity of these 

 cultures does not appear to be due to the passage of an unknown 'invisible 

 microorganism' which is finally transmitted to healthy hogs by inocu- 

 lation. Control experiments tend to show that the pathogenicity of 

 the cultures of Spirochseta suis is due to the species itself in the form of 

 spirochetes or granules. 



"Finally, in those hogs which receive the disease from cultures of 

 Spirochseta suis, the organism is present in the intestinal lesions or 

 local external lesions, as demonstrated by the dark-field examination. 



"From the above results, which have practically fulfilled Koch's 

 laws, in so far as it is possible with an organism possessing the biological 

 characteristics of spirochetes, it may logically be concluded that Spiro- 

 chseta suis is more nearly established as the specific cause of hog cholera 

 than any other known organism." 



From the foregoing it will be noted that there is still 

 some contention as to the cause of hog cholera. At this 

 time the filterable virus is usually given as the cause, but 

 future investigations may reveal faulty technic or errone- 

 ous conclusions of the experiments that have been con- 

 ducted and establish a new causative factor of hog 

 cholera. 



Source of Infection. The original source of the 

 virus of hog cholera, like the origin of other viruses and 

 pathogenic agents, is unknown. The following are the 

 principal sources of virus of hog cholera: infected swine, 

 the discharges from infected swine, the carcasses of swine 

 dead of cholera, virus used in simultaneous immunization; 

 food, water, vehicles of transportation, stock yards, and 

 any other substance or objects contaminated with the 

 discharges of infected swine, or the tissue juices or prod- 

 ucts of the carcasses of swine dead of cholera. 



From the foregoing the ease of obtaining infection is 

 readily comprehended. The virus is transmitted from an 

 infected swine on noninfected premises to other swine, or 

 to soil, food, water, bedding, and general surroundings, 

 thus practically insuring infection of other swine on the 

 same premises and other premises as well. Serious out- 

 breaks of cholera are sometimes traceable to the intro- 

 duction of a new boar, or other animal, that is infected. 



If the carcass of a sw T ine dead of cholera is permitted 

 to remain in the hog lot, other swine will become infected 



