264 AGRICULTURAL BACTERIOLOGY 



It is believed that this increased susceptibility is due to the 

 accumulation of lactic acid in the tissue. The effect of 

 lactic acid in increasing the ability of the organism to pro- 

 duce disease can be shown by injecting a weakened culture 

 that has been treated with lactic acid. The mixture will 

 produce a fatal attack, while the weakened culture alone 

 would not harm the animal. 



It is believed that the organism does not pass directly 

 from one animal to another by contact, but that the infec- 

 tion results from a common source, the soil. It is generally 

 conceded that the organism is introduced into the system 

 through puncture wounds caused by thorns, spines, and 

 grass burs, and that to take effect the organism must pene- 

 trate the subcutaneous tissue, a fact that explains the 

 greater ease with which thin-skinned animals become in- 

 fected. It is a disease primarily of the pasture ; and hence 

 appears in the Northern States only in the summer, but 

 farther South it occurs during the entire year. It affects 

 sheep and goats less frequently than cattle. 



Symptoms. The symptoms of the disease are usually so 

 characteristic that there is little likelihood of its being con- 

 founded with other causes of death. The general symptoms 

 are high fever and loss of appetite. The mucous mem- 

 branes are at first dark red, changing in the course of a 

 few hours to a dirty leaden or purplish color. 



The tumors, which appear most commonly in the thigh or 

 shoulder, are the most characteristic lesion of the disease. 

 They may be present on the neck, chest, flank, or rump 

 indeed, on any part of the body except below the knee or 

 hock joints. The tumors are at first small and painful ; 

 they increase rapidly in size. The lymph-glands in the vi- 

 cinity of the tumors become swollen. The tumor is cool 

 to the touch and painless in the center. The skin covering 

 it is dry-and parchment-like. The lack of sensation at the 



