300 SPECIFIC MICRO-ORGANISMS 



var. humanus and B. tuberculosis var. bovinus. Some, or perhaps 

 all four of these types may be eventually recognized as distinct 

 species. At present the designation as types or varieties seems 

 more appropriate. 



Bacillus Tuberculosis var. Humanus. This organism occurs 



FIG. 125. Bacillus tuberculosis in the sputum of a consumptive; stained by Ziehl 

 method. X 2100. (After Kossel.} 



in the infiltrated lung in human phthisis and also in the great 

 majority of the other tuberculous lesions in man. In the ex- 

 ternal world it does not grow naturally and passes there a more 

 or less temporary existence in discharges from the body, of which 

 the most important is the sputum. The cell is about 0.4;* in 

 width and quite variable in length, 0.5 to S.oju. The longer 



