DR. LEGEAR'S STOCK BOOK. 323 



Causes. Blackleg is causd by a bacillus, which is a micro- 

 scopic organism, or bacteria, visible only by the use of a power- 

 ful microscope. The bacilli are cylindrical or rod-like bodies 

 and have the power of indefinite multiplication, and in the body 

 of an infected animal they produce death by rapidly increasing 

 in number and producing substances which poison the body. 

 In the body they multiply in number by becoming elongated and 

 then dividing into two, each new germ continuing the same pro- 

 cess indefinitely. They will grow and multiply outside the body 

 when in a favorable locality and position for growth. Oval bodies 

 appear within the bacilli, which are called spores (seeds), and 

 which remain alive and grow and produce the disease after sev- 

 eral years of drying. They have a wonderful power of resist- 

 ance against heat and cold, as it takes boiling water to destroy 

 them. These spores often collect in sufficient numbers in feed 

 and cause serious outbreaks of blackleg among stall-fed cattle. 



There is practically no danger of a transmission of this disease 

 from one animal to another, since it is contracted on the pas- 

 tures from the ground and in the stables from the food. The 

 bacilli, if not already in the soil, finds its way on to a farm or 

 ranch in what appears at times to be the most unaccountable 

 way. Throwing carcasses of animals that have died of blackleg 

 into running streams, or shallow burial near running streams, 

 is a fertile source of infection to pastures along such streams be- 

 low. Dogs or wild animals may dig up carcasses not buried deep 

 and scatter the bacilli and spores over the pastures. M. Pasteur 

 by a series of experiments has proven that earth worms bring the 

 spores to the surface which remain a source of danger to all 

 young cattle that graze in the vicinity. Before the disease can 

 be produced the germs must gain entrance to the animal's sys- 

 tem by some means. They may enter the system through sores 

 and abrasions on the feet or legs of animals as they walk over the 

 pastures or through mud and water. The most common source 

 of entry of the bacilli is with the food and water. There may 



