METABOLISM 



419 



be made to Calmette (1936). With regard to weaker solutions Douglas and Hartley 

 (1934) found that a saline suspension containing 1 mgm. of moist bovine bacilli 

 per ml. was sterilized within 24 hours by exposure at room temperature to 0-5 

 per cent, phenol or 0-02 per cent, merthiolate. Phenol in 0-25 per cent, concentra- 

 tion failed to sterilize the suspension in 14 days, while 0-1 per cent, formol appar- 

 ently just failed to do so. In our own experience, using the cultural instead of 

 the animal inoculation method, 0-5 per cent, phenol cannot be relied on to destroy 

 all tubercle bacilli in 24 hours. In milk tubercle bacilli are killed in 20 minutes 

 at 60° C, provided it is contained in a closed vessel (for references, see Wilson 1942). 

 In an open vessel a pellicle forms on the surface which protects the organisms to 

 some extent, so that a few bacilli may escape destruction for an hour (Smith 1899, 

 Oerskov 1925, Meanwell 1927). In polluted water kept in the dark at room tem- 

 perature tubercle bacilli may remain alive for at least 3 months (Rhines 1935), 

 while in soil or cow-dung exposed on pasture land during the summer and autumn 

 in this country they may remain alive and virulent for 2 to 6 months (WiUiams 

 and Hoy 1930, Maddock 1933). The organisms are comparatively resistant to 

 drying, and provided they are protected from sunlight they may survive for 

 months under suitable conditions. In books contaminated with the sputum of 

 tuberculous patients, they may remain viable from 2 weeks to 3| months (see 

 Smith, C. R., 19426). Numerous experiments have been performed to test the 

 action of light on tubercle bacilli (Rochaix and Colin 1911, Mayer 1921, Caldwell 

 1925, Eidinow 1927, Mayer and Dworski 1932, Smith, C. R., 1942a). Most workers 

 have found that they are rapidly destroyed, if spread in a thin layer, by bright 

 sunlight, or by ultra-violet rays from a mercury vapour lamj). The most effective 

 appear to be the short ultra-violet rays. Thus bacilli suspended in saline, when 

 exposed in quartz flasks to rays of 2300-7620 A.U., were killed in 10 minutes ; 

 those exposed through window glass to rays of 3300-5720 A.U. were not com- 

 pletely killed even in 1 hour. Probably the rays shorter than 3300 A.U. are 

 the most lethal (Eidinow 1927). Blood, serum, and other proteins protect the 

 bacilli against ultra-violet light. 



Growth of tubercle bacilli in glycerine broth is inhibited by the addition of very small 

 quantities of certain aniline dyes ; thus a concentration of 00004 per cent, thioflavine 

 or 00002 per cent, methylene blue entirely prevents growth ; smaller quantities have 

 little or no effect. Thymol is active in a concentration of 0*004 per cent. ; most metals 

 in coUoidal suspension, however, are inactive even in a concentration of 10 per cent 

 (Karwacki and Biernacki 1925). 



Metabolism. — The optimum hydrogen-ion concentration for growth in 4 per 

 cent, glycerine broth is said by Ishimori (1924) to lie between the following points : 



Human type of tubercle bacillus 

 Bovine ,, ,, ,, ,, 



Cold-blooded ,, „ „ 



Rabinowitsch's butter bacillus . 

 Timothy grass bacillus 

 Moeller's grass bacillus ii. 



pH 7-4-8-0 

 pH 5-8-6-9 

 pH 6'2-7-7 

 pH 5-7-8-5 

 pH 7-5-9-1 

 pH 7-4-7-7 



Dernby and Naslund (1922) found that growth of human and bovine tubercle 

 bacilli in 3 per cent, glycerine veal broth occurred between pH 4-5 and 8-0, the 

 optimum being pH 6 0-6-5 ; their figures, it will be seen, do not agree with those 



