'S TUBERCULIN. 



249 



and in ingestion, tubercle bacilli may lodge about the 

 pharynx and thus come to infect the pharyngeal lymphoid 

 tissue, tonsils, etc., tubercular lesions of these parts being 

 much more frequent than was formerly supposed. Thence 

 the cervical lymphatic glands may become infected, and 

 afterwards other groups of glands, bones, or joints, and 

 internal organs. 



Koch's Tuberculin. We have seen that the pathology 

 of tuberculosis indicates that the tubercle bacillus can act 

 on tissues with which it is not immediately in contact, and 

 therefore it is natural to ask whether it, like other organisms, 

 produces definite toxic bodies. What knowledge we have 

 of the latter is secondary to the bringing forward by Koch 

 in 1890-91 of a substance called " tuberculin," which he 

 introduced as a curative agent for tubercular affections. 

 He had observed that if in a guinea-pig suffering from the 

 initial local induration occurring after subcutaneous inocu- 

 lation with tubercle bacilli, a second subcutaneous inocula- 

 tion of tubercle bacilli, or of dead cultures of the same, 

 was practised in another part of the body, superficial 

 ulceration occurred in the primary tubercular nodule, the 

 wound healed, and the animal did not succumb to tuber- 

 culosis. This reaction was further studied by means of the 

 above mentioned tuberculin, which consisted of a glycerine 

 bouillon culture of tubercle in which the bacilli had been 

 killed by heat, and which had then been concentrated 

 by evaporation. It thus contains the dead and often 

 macerated bacilli, the substances indestructible by boiling 

 which existed in these bacilli, non- volatile products 

 formed by them from the food material when alive, 

 and the concentrated remains of the bouillon and 

 glycerine. The injection of .25 c.c. of tuberculin into a 

 healthy man causes, in three to four hours, malaise, tend- 

 ency to cough, laboured breathing, and moderate pyrexia ; 

 all of which pass off in twenty-four hours. The injection 

 (the site of the injection being quite unimportant), how- 

 ever, of .01 c.c. into a tubercular person gives rise to 

 similar symptoms, but in a much more aggravated form, 



