TUBERCULOSIS. 22Q 



soon surrounded with a zone of newly-formed contracting 

 fibrillar tissue, by which it is perfectly isolated. In such 

 isolated masses lime-salts are commonly deposited. Some- 

 times this process is perfected without the destruction of 

 the bacilli, but with their incarceration and inhibition. 

 Such a condition is called latent tuberculosis, and may at 

 any time be the starting-point of a new infection and lead 

 to a fatal termination. 



In 1890, Koch announced some observations upon toxic 

 products of the tubercle bacillus and their relation to the 

 diagnosis and treatment of tuberculosis, which at once 

 aroused an enormous but, unfortunately, a transitory 

 enthusiasm. 



These observations, however, are of capital importance. 

 Koch observed that when guinea-pigs are inoculated 

 with a mixture containing tubercle bacilli the wound 

 ordinarily heals readily, and soon all signs of local dis- 

 turbance other than enlargement of the lymphatic glands 

 of the neighborhood disappear. In about two weeks there 

 occurs at the point of inoculation a slight induration which 

 develops into a hard nodule, then ulcerates, and remains 

 until the death of the animal. If, however, in the course 

 of a short time the animals are reinoculated, the course 

 of the process is altogether changed, for, instead of heal- 

 ing, the wound and the tissue surrounding it assume 

 a dark color and become obviously necrotic, and ulti- 

 mately slough away, leaving an ulcer which rapidly and 

 permanently heals without enlargement of the lymph- 

 glands. 



Having made this observation with injected cultures 

 of the living bacillus, Koch next observed that the same 

 change occurred when the secondary inoculation was 

 made with pure cultures of the dead bacilli. 



It was also observed that if the material used for the 

 secondary injection was not too concentrated and not 

 too often repeated (only every six to forty-eight hours), 

 the animals thus treated improved in condition, and, 

 instead of dying of the tuberculosis induced by the 



