CHAPTER XXIII. 



THE TUBERCLE BACILLUS GROUP: HUMAN, BOVINE, 



AND AVIAN. 



THE ACID-FAST GROUP. 



THERE is a well-defined group of bacteria characterized by the 

 relatively large amounts of lipoidal substances contained within their 

 bodies. These lipoidal or waxy substances confer upon the members 

 of the group distinctive staining reactions; ordinary dyes do not 

 stain them at all, or at best slowly. The more intense stains con- 

 taining a mordant, as carbol-fuchsin, penetrate the waxy envelope, 

 especially when heat is applied; once stained the bacteria retain 

 the dye tenaciously even after treatment with mineral acids. This 

 resistance to decolorization with acids has led to the name the 

 Acid-fast group. 



Included within the group of acid-fast bacteria are saprophytic 

 types found rather commonly in hay and manure; parasitic organ- 

 isms found upon the surface of the body, as the smegma bacillus and 

 the nasal secretion bacillus of Karlinski; and exquisitely pathogenic 

 bacteria, Bacillus tuberculosis and Bacillus leprse. The basis of 

 classification therefore is chemical rather than morphological, and in 

 this sense the definition of the acid-fast organisms does not follow a 

 strictly natural system. 



Types of Tubercle Bacilli. Four types of tubercle bacilli are 

 recognized which are pathogenic respectively for man, cattle, birds, 

 and for fishes and reptiles; the human, bovine, avian, and ichthic 

 varieties. Considerable discussion has arisen concerning the identity 

 of the human, bgvine, and avian varieties, some authorities claiming 

 that they are identical, although modified somewhat by their con- 

 tinuous sojourn in a series of animals of the same kind. The evidence 

 for this view is arrayed around the observation that tubercle bacilli 

 of undoubted bovine type occasionally are isolated from tuberculous 

 lesions in man (chiefly in children, infrequently in adults). On the 

 other hand human bacilli are less commonly found in progressive 

 tuberculous lesions of cattle. In spite of many attempts to change 



