328 TUBERCULOSIS AS A TYPE OF BACTERIAL DISEASE 



the bacillus tuberculosis discovered by Koch is the only immediate 

 cause of all forms of human tuberculosis. In the majority of cases 

 the micro-organism is met with in the form of slender rods, but imder 

 certain conditions at present imperfectly understood, the micro-organism 

 may show filaments, true dichotomous branching and club forma- 

 tion, and, in the tissues, especially in experimental tuberculosis, it may 

 assume a radiate arrangement — characters which from a taxonomic 

 point of view bring it into close relation with a large group of micro- 

 organisms variously designated Streptothricese, Gospora, ITocardiacese, 

 and more recently Actinomycetes (Lachner-Sandoval). According 

 to all experience, the tubercle bacillus is an aerobic facultative 

 parasite, which grows extremely slowly outside the body, and the fact 

 that for its growth it requires a relatively high temperature is against 

 the supposition that the tubercle bacillus multiplies extra-corporeally, 

 at least in temperate climates. 



Morphological differences are found under different circumstances, 

 and within limits variation occurs according to the environment. 

 The filaments, threads, and true branching forms of old cultures have 

 been met with, though only occasionally, in sputum. Clubbed 

 actinomycotic forms have also been described. On these facts some 

 bacteriologists are disposed to look upon the tubercle bacillus as 

 belonging to the higher bacteria (Plate 18). 



Gultivation on Various Media. — Koch inoculated solid blood serum 

 with tubercular matter from an infected lymphatic gland of a guinea- 

 pig, and noticed the first signs of growth in ten or twelve days in 

 the form of whitish, scaly patches. These enlarged and coalesced 

 with neighbouring patches, forming white, roughened, irregular masses. 

 The blood serum is not liquefied. Nocard and Eoux showed that by 

 adding 5 to 8 per cent, of glycerine to the media commonly used in the 

 laboratory, such as nutrient agar or broth, better growth is obtained. 

 In glycerine broth abundant growth appears at the end of seven 

 or eight days, and eventually cultures taken from glycerine broth 

 will be found to grow well in ordinary bouillon. A pellicle generally 

 forms. On glycerine agar, minute crumb-like colonies of whitish- 

 yellow colour appear in six to twelve days. Later, the whole growth 

 turns browner in colour, and is sometimes dry, sometimes moist, in 

 appearance depending on age of culture, and consistence of medium. 

 Ultimately, the discrete colonies coalesce and form a lichenous 

 growth. By continuous sub-culture on glycerine agar the virulence 

 of the bacillus is diminished. But in fifteen days after inoculation of 

 the medium the culture equals in extent a culture of several weeks' age 

 on blood serum. In alkaline broth to which a piece of boiled white 

 of egg was added, Klein obtained copious growth, and found that 

 continued sub-culturing upon this medium also lessens the virulence. 

 On potato the tubercle bacillus grows well in crumb-like masses. 



