VACCINE-THERAPY 177 



The Bacillus of Tuberculosis. 



This bacillus, in conjunction with B. leprse, Johne's 

 bacillus, and certain non-pathogenic bacteria isolated from 

 faeces, hay, milk, butter, and other sources, have common 

 staining and morphological characters, which associate 

 them under one group, known as the "acid-fast group." 

 As the term implies, they possess the power of retaining 

 stains which resist the decolorizing action of strong acids. 

 They do not stain readily with ordinary aniline dyes, but 

 when stained, they become " acid- fast." 



The members of this group are all slender rods, non- 

 motile, having neither capsules nor spores, and are Gram- 

 positive. 



Their slight variations, morphologically and culturally, 

 and their considerable differences, so far as their patho- 

 genesis goes, serve to differentiate the various species. 



The B. tuberculosis is a slender rod, frequently bent, with 

 rounded ends. In length it varies from 0*2 to 3"5 /x. It may 

 stain irregularly, giving the bacillus a beaded appearance. 



Save for Johne's bacillus, the other bacteria of the acid- 

 fast group are non-pathogenic to animals, and their presence 

 in animal tissues may be defined as accidental. It is probable 

 they are more commonly present as such than we are inclined 

 to believe. In any case, this probable fact should make us 

 the more careful in drawing our conclusions and giving 

 our opinions. Where one is permitted to do so by law, and 

 time for giving an opinion is unlimited, the presence of 

 tubercle bacilli in morbid material can be most satisfactorily 

 settled by the biological test. 



Methods for staining the Bacillus of Tubercle. 



Ziehl-Neelsen's Method. — The materia morbi having been 

 collected with the usual careful precautions to prevent 

 outside bacterial contamination, and subjected to the 

 methods necessary to facilitate the easy finding of the 

 bacteria, as already described, a loopful of the material is 

 taken up by a sterile platinum loop, and spread by the 



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