278 



BLACK LEG 



a number of the other Western States are badly infected. 

 Many of the states east of the Mississippi river have infected 

 localities, but in a few of the Eastern and Southern states it 

 seems not to exist. During the last few years infected locali- 

 ties have been found in New York where there has been an 

 annual loss from this disease, but where prior to recent inves- 

 tigations the cause of death has been attributed to poisoning. 



§ 20I. Etiology. Black leg is caused by Bacillus chau- 

 veaui. This organism varies from 3 to 6/< in length and from 

 0.5 to I.// in width. The ends are rounded and it produces 

 spores. It stains readily with ordinary aniline dyes and also 

 after the gram method. In cultures long involution forms are 

 often observed. It is anaerobic. In suitable culture media 

 under anaerobic conditions or in animal tissues (other than 



Fig. 63. Bacillus of black leg ivith flagella and ivith spores 



{after Hutyra). 



blood) it multiplies rapidly with the evolution of gas. The 

 presence of spores renders it very resistant to natural destruc- 

 tive agencies and to the common disinfectants. The bacillus 

 of black leg or its spores are supposed to gain entrance to the 

 tissues of animals through abrasions of the skin or, possibly, 

 the raucous membranes of the mouth or intestine. 



The period of inciihation is not known in cattle but it is 

 supposed to be very short. Guinea pigs inoculated with a 

 culture of the organism die in from one to three days. 



