MYCOBACTERIACE^ : THE TTJBERCI,E BACILLUS 317 



\ 



particular interest. This makes up from 

 8 to 40 per cent of the dry substance, less 

 in young and more in old cultures. The 

 acid-proof staining property depends upon 

 this waxy substance, for the bacilli from 

 which it has been extracted by ether- 

 alcohol are no longer acid-proof while the 

 wax itself exhibits this peculiarity of 

 staining. It is also known that the bacilli 

 in young cultures are on the whole less 

 acid-proof than those from old cultures in 

 which chemical analysis shows a greater 

 concentration of the waxy substance. The 

 protein substances, largely nuclein, make 

 up about 25 per cent of the dry cell sub- 

 stance. Several other constitutents of the 

 cell have been identified. As in the case 

 of other bacteria the chemical composition 

 varies within rather wide limits according 

 to the nutritive medium, conditions of 

 growth and especially the age of the 

 culture. 



The poisons of the tubercle bacillus 

 exist to a large extent in an inactive form 

 in the culture fluid and more particularly 

 as an undissolved constituent of the 

 bacterial cell bodies. Culture filtrates 

 exert little or no effect upon injection into 

 normal animals. The dead bacilli, how- 

 ever, give rise to local inflammation and 

 in many instances stimulate the formation 

 of typical tubercles at the point where J^^^^^^^H:^;^ 

 they lodge. Evidently the poison is set agar several months old. 



. , , . , , , (From McFarland after 



free from some substance m the dead curtis.) 

 cells by the action of the tissue cells or 



