94 A MANUAL OF BACTERIOLOGY 



Exercise 134. Tuberculosis (Consumption, Phthisis) 



This disease is the greatest scourge of the human race. In 

 1900 about one ninth of all deaths from known causes in the 

 United States were due to this disease. Small nodules, or tuber- 

 cles, are so uniformly observed in all advanced stages of the 

 disease in animals that their presence has given the name to the 

 disease. The tubercle eventually breaks down, the central por- 

 tion becomes necrotic, caseation sets in, and then the caseous 

 mass softens, probably due to the toxic action of bacterial prod- 

 ucts. In many cases a deposit of calcium salts finally takes place 

 in the tubercle, and it is converted into a hard, dry, friable body 

 which may be entirely walled off from the neighboring tissue. 



Besides man the disease attacks cattle, swine, birds, and other 

 animals. Among these animals the ravages of the disease are at 

 times very severe. 



Tuberculosis may attack almost any tissue or organ in the 

 body. The lungs constitute the seat of the most common infec- 

 tion, but the intestines, the mesenteric glands, the lymph glands 

 of the head and neck, the portal glands and liver, the skin, the 

 bones, and the urogenital system are frequently attacked. lie- 

 sides the lesions on important organs, the tuberculosis organism 

 produces a slow toxemia which works injury to the whole of the 

 infected body. 



The ways of infection are usually four: (1) the respiratory 

 tract ; (2) the alimentary tract ; (3) inoculation (rare) ; (4) pre- 

 natal infection. The first two are more common, so far as we know. 



Tuberculin is a mixture of the toxins produced by B. tuher- 

 culosiz in artificial cultures. A glycerin-broth culture of the 

 organism is sterilized in steam, then concentrated by evaporation 

 on a water bath, then filtered through paper and a Berkefeld 

 filter. If it is to be kept, a preservative is added. Tuberculin is 

 of use in making a diagnosis. Its injection into man or animals is 

 followed within two to ten hours by a rise in temperature, which 

 continues for a few hours and then disappears. Many modifica- 

 tions of the original method of preparing tuberculin are now 

 employed. 



