Biological Therapy 



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becoming diffuse and non-sensitive. The swellings develop 

 a marked crepitation beneath which is a fetid, sweetish fluid 

 admixed with blood. These swellings are never observed 

 below the hock or knee nor on the tail. Crepitant swellings 

 may become apparent about the mouth and throat and these 

 are followed by dyspnoea and by pneumonia in cases where 

 death is postponed although death usually occurs in twelve 

 to forty-eight hours. In some cases large areas of the body 

 particularly over heavily muscled areas become covered 

 with edematous and crepitant swellings. 



LESIONS. Intense bloating and gas formation, par- 

 ticularly about the tumors, is characteristic of blackleg. A 

 bloody foamy fluid may exude through the skin and from 

 any of the natural openings. Tissue, other than that actu- 

 ally affected, may assume a scarlet hue when exposed to the 

 air. The affected muscles emit a rancid sweetish gas and a 

 foamy dark fluid which is mixed with disintegrated muscle. 



The post mortem lesions are conflned largely to the 

 affected parts, other portions of the body being largely 

 devoid of pathological changes. 



PREVENTION. Biologies which in the past were ex- 

 tensively used for the prevention of blackleg have gradu- 

 ally been supplanted by newer products which are less haz- 

 ardous and which can be more accurately standardized. Of 

 these newer products Blackleg Filtrate and Blackleg Ag- 

 gressin are the ones now in general use. Both products 

 are of a similar biological nature since both are aggressins, 

 the one a natural aggressin produced in the diseased mus- 

 cles of affected animals while the other (flltrate) is produced 

 in the laboratory in suitable culture media. Blackleg fil- 

 trate has been used to immunize millions of cattle in many 

 countries, particularly in Japan and America. It is used 

 in Japan to the exclusion of all other products with entirely 

 satisfactory results. 



The immunity conferred by this product is not exceeded 

 in intensity nor in its duration by any other biologic capable 

 of immunizing against this disease. The average immunity 

 conferred by these two products is of approximately one 

 year's duration. In heavily infected districts it is advisable 

 to reinforce the immunity by a second injection in six 

 months. Blackleg Filtrate should be used only on healthij 

 animals at least seven to ten days before exposure. 



