676 Tuberculosis 



Behring* found that this acid contained a his ton-like body whose 

 removal left chemically pure tuberculinic acid. One gram of this 

 acid is capable of killing a 600-gram guinea-pig when administered 

 beneath the skin. One gram is fatal to 90,000 grams of guinea- 

 pig when introduced into the brain. If injected into tuberculous 

 guinea-pigs it is much more fatal, i gram destroying 60,000 when 

 injected subcutaneously and 40,000,000 when injected into the 

 brain. 



Levenef also found free and combined nucleinic acid varying 

 in phosphorus content from 6.58 to 13.19 per cent. He also found 

 a glycogen-like substance that reduced Fehling's solution when 

 heated with a mineral acid. 



Toxic Products. — In 1890 KochJ announced some observations 

 upon the toxic products of the tubercle bacillus and their relation 

 to the diagnosis and treatment of tuberculosis, which at once aroused 

 an enormous though transitory enthusiasm. The observations are, 

 however, of great importance. Koch found that when guinea-pigs 

 are inoculated with tubercle bacilli, the wound ordinarily heals 

 readily, and soon all signs of local disturbance other than enlarge- 

 ment of the lymphatic glands of the neighborhood disappear. In 

 about two weeks, however, there appears, at the point of inocula- 

 tion, a slight induration, which develops into a hard nodule, ulcer- 

 ates, and remains until the death of the animal. If, however, in a 

 short time the animals be reinoculated, the course of the local 

 lesion is changed, and, instead of healing, the wound and the tissue 

 surrounding it assume a dark color, become obviously necrotic, and 

 ultimately slough away, leaving an ulcer which rapidly and per- 

 manently heals without enlargement of the lymph-glands. 



This observation was made by injecting cultures of the living 

 bacillus, but Koch observed that the same changes also occur when 

 the secondary inoculation is made with killed cultures of the bacilli. 



It was also observed that if the material used for the secondary 

 injections was not too concentrated and the injections not too often 

 repeated (only every six to forty-eight hours), the animals treated 

 improved in condition, and continued to live, sometimes (Pfuhl) as 

 long as nineteen weeks. 



Tuberculia. — Koch also discovered that a 50 per cent, glycerin 

 extract of cultures of the tubercle bacillus — tuberculin — produced 

 the same effect as the dead cultures originally used, and announced 

 the discovery of this substance to the scientific world, in the hope 

 that the prolongation of life observed to follow its use in the guinea- 

 pig might also be true of man. 



The active substance of the "tuberculin" seems to be an al- 

 buminous derivative (bacterioprotein) insoluble in absolute alcohol. 



* "Berliner klin. Wochenschrift," xxxvi. 



t "Jour, of Med. Research," i, 1901. 



t "Deutsche med. Wochenschrift," 1891, No. 343. 



