CHAPTER XXX. 



THE BACILLUS OF TUBERCULOSIS TUBERCULIN TESTS BOVO- 



VACCINE THE INTERTRANSMISSIBILITY OF BOVINE AND 



HUMAN TUBERCULOSIS AVIAN TUBERCULOSIS. 



Morphology. The tubercle bacillus is a rod-shaped organism, 

 generally rather slender when found in human tuberculosis, more 

 plump in the bovine type, 1 and commonly even more coarse in the 

 avian type. It measures from 1.5 to 3.5 micra in length and 0.2 to 

 0.5 micron in breadth. It frequently occurs in pairs, the two individ- 

 uals may or may not be in direct contact. When bacilli are numerous 

 in sputum, pus, urine, or other fluid or semifluid tubercular products 

 they often present themselves in parallel groups or clusters. The 

 bacilli often have a beaded, granular appearance which is at times so 

 pronounced that beginners gain the impression that they are dealing 

 with short chains of streptococci. Under some conditions branching 

 forms are seen; this proves that the organism of tuberculosis is perhaps 

 not a bacillus, but more properly a member of the streptothricse to 

 which the ray fungus or actinomyces belongs. The bacilli frequently 

 show in their interior unstained, oval, or slightly biconcave spaces, 

 which were formerly mistaken for spores. It is now unanimously 

 agreed that the tubercle bacillus does not form spores, because the 

 forms which show these unstained spaces are not more resistant than 

 the uniformly stained bacilli. This fact indicates the absence of the 

 most important characteristics of the true spore namely, its greater 

 resistance to antiseptics, higher temperatures, drying out processes, 

 etc. The tubercle bacillus is not motile and does not possess flagella. 

 It does, however, possess a capsule containing a wax-like substance 

 to which the bacillus owes two remarkable features namely, its 

 peculiar staining properties and its resistance, which is greater than 

 that of most other non-sporulating pathogenic bacteria. It is also 

 more resistant to drying out than most of the latter. 



Staining Properties. On account of the tough, tenacious wax- 

 containing capsule, which surrounds the tubercle bacillus, it cannot, 

 like most other pathogenic bacteria, be stained with the ordinary 

 watery anilin stains. It requires a more intense stain, which either 

 must act for a considerable time or be heated to intensify its action. 

 After once having taken the stain, however, the tubercle bacillus 

 holds it very firmly against the decolorizing action of dilute acids, 



1 The difference between the human and bovine types of the tubercle bacillus will be considered 

 more fully under the discussion of the intertransmissibility of human and bovine tuberculosis. 



