TUBERCULOSIS. 189 



but acts upon the living tuberculous tissue. In the 

 description of the tissue-changes already given it has 

 been shown that the tubercle bacillus effects the coagu- 

 lation-necrosis of the cells, but does not derive its nutri- 

 ment from the dead tissue. As the cells die and are 

 incorporated in the necrotic mass, the bacilli find the 

 conditions of life unfavorable, and likewise seem to die. 

 The active bacilli, therefore, are always found at the mar- 

 gins of the tuberculous tissues, where the cells are fairly 

 active. The necrosis is due to bacillary poisons. When 

 tuberculin is injected into the organism the result is to 

 double the amount of poisonous influence upon the cells 

 surrounding the bacilli, to destroy their vitality, to re- 

 move the favorable conditions of growth from the organ- 

 ism, and to leave it for a time checkmated. 



Virchow, who well understood the action of the tuber- 

 culin, soon showed that as a diagnostic and therapeutic 

 agent in man its use was attended with great danger. 

 The destroyed tissue was absorbed, and with it the bacilli 

 were likewise absorbed and transported to new areas, 

 where a rapid invasion occurred. Old tuberculous lesions 

 which had been encapsulated were softened, broken 

 down, and became sources of dangerous infection to the 

 individual, so that, a short time after its enthusiastic 

 reception as a "gift of the gods," tuberculin was placed 

 upon its proper footing as a diagnostic agent valuable in 

 veterinary practice, but dangerous in human medicine, 

 except in cases of lupus and other external forms of the 

 disease where the destroyed tissue could be discharged 

 from the surface of the body. 



The method of preparation of tuberculin is rather 

 simple. Small flasks exposing a considerable surface of 

 liquid are filled with about 25 c.cm. of bouillon contain- 

 ing about 4 per cent, of glycerin. The bouillon is prefer- 

 ably made with calf- instead of ox-meat. When thor- 

 oughly sterile the surfaces are inoculated with pure 

 cultures of the tubercle bacillus and are stood in an 

 incubator. In the course of two weeks a slight surface 



