MYCOBACTERIACE^: THE TUBERCLE BACILLUS 319 



specific 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.^ 

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

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

 btoth. 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 "Boi^illon filtr6" of Denys is 

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

 glycerin-broth culture of the tubercle bacillus. It resemblesKoch'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 inocu- 

 lation 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, 0.00 1 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 tuberculosis, 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 

 recognized as a contagious disease by the ancients. Laennec,^ 



iLowenstein in KoUe und Wassermann, Handbuch, 191 2, Bd. V, S. 554-555. 

 " For a history of tuberculosis see Landouzy : Cent ans de phtisiologie, 1808-1908, 

 Sixth Intemat. Cong, on Tuberculosis, Special Volume, pp. 145-189. 



