288 ACUTE GENERAL INFECTIOUS DISEASES 



in the droppings of cattle. Morphologically and culturally 

 the black-leg bacillus so closely resembles the malignant 

 edema bacillus that differentiation is very difficult. 



Natural Infection. — (a) Through wounds in the skin and 

 mucous membranes. Stubble, thorns, spines, barbed wire, 

 etc., causing small punctured wounds, which on account of 

 their character are most apt to become infected with soil, 

 etc., containing the rods or spores. 



(b) Through the digestive tract from the ingestion of con- 

 taminated food and water. The presence of the black-leg 

 tumor in the throat, bowels, and other internal organs, and 

 the occurrence of outbreaks in stable-fed animals speak for 

 this mode of infection. The disease is miasmic and does not 

 spread from animal to animal. Black-leg carcasses, however, 

 if not rendered harmless by cremation or deep burial, con- 

 tribute toward the perpetuation of the infection by reinfecting 

 the soil. 



Symptoms. — Black-leg is seen almost exclusively in cattle. 

 Probable cases in sheep and swine have been recorded. Opin- 

 ions differ concerning its occurrence in horses, but no authentic 

 data in this regard are available. Black-leg is a disease of 

 young, full-blood, or high-grade cattle. It is rarely noted in 

 animals under six months or over two years of age. The 

 period of incubation is usually one to three days, occasionally 

 longer (five days). The symptoms are both (a) general and 

 (6) local. 



General Symptoms. — Fever, the temperature reaching 107° 

 F., refusal of food, suspended rumination, and great mental 

 depression. Quite often the first symptom noticed is lame- 

 ness in one limb. 



Local Symptoms. — Following or sometimes preceding the 

 general symptoms, external swellings appear in the region of 

 the thigh, croup, loins, shoulder, breast, and throat. While 

 at first small, the tumefactions rapidly increase in size until 

 a large portion of the body is involved. In rare cases the 

 swellings may be internal and located in the tongue or 

 pharynx or bowel (colic symptoms) . At first the tumors are 

 firm, hot, and tender, but later, provided the animals live 

 long enough, cooler, non-sensitive, the overlying skin hard 



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