ACID-FAST GROUP 



317 



and the intestines commonly show lesions. In a certain small 

 percentage of tuberculous cows, variously estimated from a frac- 

 tion of 1 to 5 per cent., tuberculous lesions may be found in the 

 udder. Any and all of the organs of the body may be infected. 

 Swine are most commonly infected in the lymph-glands of the 

 neck (swine scrofula) , and in the abdominal organs and the lungs. 

 Avian tuberculosis most frequently attacks the abdominal organs, 

 particularly the liver and spleen, more rarely the lungs. 



Immunity. No true toxin has been demonstrated for the 

 tubercle bacillus. Endotoxins are produced. These are liberated 





i 



Fig. 130. Section of a tubercular intestinal wall showing the bacilli and giant- 

 cells (Chausse). 



from the cell with difficulty because of its composition and slow 

 dissolution. Specific agglutinins and precipitins have been de- 

 monstrated in the blood of infected individuals and in immune 

 serum. Opsonins, both normal and immune, have been shown to 

 occur. The development of bacteriolysins has not been satis- 

 factorily demonstrated. 



Methods of active immunization are all dependent upon the use 

 of killed or attenuated bacteria or their products. The name tuber- 

 culin is given to any suspension of dead tubercle bacilli or a solu- 



