356 VETERINARY BACTERIOLOGY 



rod. These characters enable one readily to differentiate it from 

 the B. tetani. When the spores are central, the spindle-shaped 

 swollen cell is called a clostridium. The organism is easily stained 

 by the common aqueous anilin dyes, but is gram-negative. This 

 reaction to Gram's stain is a little uncertain, some cultures retain- 

 ing the stain to some degree. 



Isolation and Culture. The organism may be readily isolated 

 in pure cultures from the tissues infected. Plates may be poured 

 and kept under anaerobic conditions. The colonies are spherical, 

 or somewhat irregular, with microscopic radiations. Dextrose 

 gelatin is an exceptionally favorable medium. In a shake culture 

 the colonies appear in the lower portion of the tube, each usually 

 with its gas-bubble, and surrounded by a liquefied area. Bouillon 

 is clouded, gas is produced, and a flaky white deposit forms. The 

 reaction in milk is somewhat variable; according to most authori- 

 ties, it produces acid, coagulates, and later proteolyzes the casein. 



Physiology. The optimum growth temperature is about blood- 

 heat, but good growth occurs at room-temperatures. The organ- 

 ism is a strict anaerobe. Concerning its other physiological char- 

 acters, there is considerable disagreement among investigators. 

 This may be due to the fact that there are strains which react very 

 differently, and may constitute distinct varieties. Grassberger 

 and Schattenfroh claim that the organism shows considerable 

 variability, and that certain characters are easily lost. The 

 spores are quite resistant to desiccation. Heating for some hours 

 at 100 is necessary certainly to destroy them. Gas is produced 

 from carbohydrates, and probably also from proteins. According 

 to some authorities, butyric acid is produced. 



Pathogenesis. Experimental Evidence. Inoculation of pure 

 cultures into laboratory animals results in death, with production 

 of many of the characteristic symptoms of blackleg, particularly 

 the edema about the point of inoculation. The disease may also 

 be produced in cattle, so that there is no doubt as to the etiological 

 relationship of this organism to the disease. 



Character of Disease and Lesions Produced. Blackleg in cattle 

 is characterized by a swelling, edema, and emphysema of the 

 muscles and the subcutaneous tissues of the infected part. Infec- 

 tion appears most commonly in the shoulder or hindquarter. 



