148 PRINCIPLES OF VETERINARY SURGERY 



ing the disease itself, and thus causing out-breaks that would 

 otherwise not have occurred. 



It is very evident that the immunity against black-leg is 

 strictly one of degree. It is very slight in the young ox, but 

 increases with age, and is never entirely complete. It has 

 been shown that non-receptive animals can be artificially in- 

 fected by artificially increasing the virulence of the bacteria 

 or by artificially diminishing the resisting forces of the 

 tissues at the seat of inoculation. Absolutely refractory ani- 

 mals, artificially immunized animals and naturally immune 

 animals, can be infected by injecting the tissues with cul- 

 tures associated with certain harmless bacteria, notably the 



Fig. 18. 

 Sporulation of B. Oedematis Maligni. 



bacillus prodigiosus. And finally, lactic acid added to the 

 culture renders successful infection of non-receptive sub- 

 jects, possible. 



Diagnosis. — The emphysematous symptom and the 

 rapid course of black-leg brings out a clinical tableau that 

 bears considerable resemblance to malignant oedema, from 

 which disease it must always be dififerefttiated. The fact, 

 however, that the former disease attacks chiefly young cat- 

 tle, and usually a number of them simultaneously, seldom 

 leaves any room for doubt. Malignant oedema cases are al- 

 ways single cases. It would indeed be a rare coincidence 

 to see two animals attacked at the same time, considering 



