BACTERIACE.E : THE TUBERCLE BACILLUS 305 



kulin"). Chemical study of tuberculin has shown that the spe- 

 cific active substance is a thermostable, dialyzable substance, 

 insoluble in alcohol, which gives most of the protein reactions 

 but not the biuret test. It is digested by pepsin and by trypsin. 1 

 Koch's new tuberculin, better known as tuberculin B . E. ("Bacillen- 

 emulsion") is made from the solid bacterial growth on glycerin 

 broth. The growth is pressed between filter papers, dried and 

 then pulverized in a ball mill for about three months, then sus- 

 pended in 50 per cent aqueous solution of glycerin, 0.002 gram 

 of the powder to each cubic centimeter. Finally it should be 

 sterilized by heating to 60 C. for 20 minutes. This tuberculin 

 is a suspension, not a solution, and must be thoroughly mixed 

 each time before use. Numerous other tuberculins have been 

 prepared, of which perhaps the " Bouillon filtre" of Denys is 

 the most important. It is the porcelain filtrate of the unheated 

 glycerin-broth culture of the tubercle bacillus. It resembles 

 Koch's old tuberculin except that it is not heated and is not 

 concentrated. 



Inoculation of animals with B. tuberculosis gives rise to typical 

 tuberculous lesions and death in most mammalian species. 

 The guinea-pig is very susceptible to subcutaneous injection 

 but not readily infected by the alimentary route. The lesions 

 are usually well developed four or five weeks after subcutaneous 

 inoculation and death occurs as a rule in 6 to 12 weeks. Rabbits 

 are less susceptible to inoculation with the human type and they 

 usually recover when injected with small doses of a culture, 

 o.oo i gram intravenously. Cattle are quite immune to this 

 organism. Large doses of cultures or of sputum have been 

 injected into calves and older bovines without producing tubercu- 

 losis, and quarts of tuberculous sputum have been fed to bovine 

 animals with negative results. 



Tuberculosis is, economically, the most important human 

 disease. Approximately one death in every three between the 

 age of 20 and 45, the active period of life, is due to it. It was 

 1 Lowenstein in Kolle und Wassermann, Handbuch, 1912, Bd. V, S. 554- 555. 



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