BACILLUS TUBERCULOSIS 33 



ments which had previously been made with impure 

 material showed that the bacillus of Koch, contained 

 in the inoculated matter, was the cause of the tuber- 

 cular lesions produced, and confirmed the inocula- 

 bility and infectiousness of the disease. 



Subsequently Koch demonstrated in the cultures, 

 or rather in extracts of the bacilli, a toxic material, 

 " tuberculin," which has a specific inflammatory in- 

 fluence on tubercular tissues, and with which 

 attempts have been made to cure or arrest the 

 disease. 



The bacillus (Figs. 25-29) is straight or slightly 

 curved, usually round-ended, and varying in length 

 from 1*3 to 3 '5 /u that is to say, about a quarter to 

 half the diameter of a red blood cell, and is of 

 extreme tenuity ('2-*4 p). Originally demonstrated 

 by staining with alkaline met hylene- blue, it was 

 almost at once shown by Ehrlich to have a so-called 

 specific staining reaction, which displayed the bacillus 

 clearly and differentiated it from all but two or 

 three other micro-organisms (B. Leprse, B. Smeg- 

 matis). This specific reaction depended upon the 

 fact that, unlike nearly all other organisms, the 

 tubercle bacillus, when strongly stained with fuchs- 

 ine or gentian-violet, resisted the decolorising action 

 of strong acids (e.g., 25 per cent, nitric acid). 



