THE SPOEE-BEAEING EODS 361 



means of peritrichous flagella. Under suitable conditions in 

 cultural media spores are produced, sometimes centrally 

 located but more frequently near the poles. The spores are 

 elliptical in shape and cause the cell to swell some- 

 what. The organism is easily stained and usually Gram- 

 positive. 



Cultural Characters. — Culture is somewhat diiScult 

 because the organisms grow only under anaerobic condir 

 tions. Cultures grow best in a medium that is somewhat 

 alkaline. Gas is produced from dextrose. Bouillon be- 

 comes clouded, and in the presence of carbohydrates, gas is 

 produced. 



Physiology. — The organism grows best at blood heat 

 but readily also at room temperatures. It is 'strictly ana- 

 erobic; the spores are resistant to drying, having been 

 found to live for j^ears in this condition. 



Pathogenesis. — Blackleg occurs niost frequently in 

 young cattle, but rarely in calves or in adult animals. The 

 disease is characterized by swelling, softening, and gas pro- 

 duction in the muscles and hemorrhagic edema of the parts 

 which have been infected. It occurs most frequently in 

 the shoulder or hind quarter. The presence of gas is usu- 

 ally demonstrable by the crackling sound which is produced 

 when the thumb is drawn quickly across the skin of the 

 infected parts. After the death of the animal the tissues 

 may be generally invaded and the body become swollen 

 due to the development of gas. When the tissues infected 

 are sectioned they are found to be blackened and hemor- 

 rhagic. The disease is usually fatal. 



Immunity. — According to some authors, the Clostridium 

 chauvmi produces a true toxin, for which an antitoxin may 

 be prepared. It has been found, however, that the antitoxin 

 is of relatively little use in the immunization of animals. 

 Much more commonly practiced is active immunization by 

 means of vaccine. The standard method of preparation 



