370 A MANUAL OF BACTERIOLOGY 



and facultatively anaerobic, and thrives best at a tem- 

 perature of 37 C. or thereabouts, but development even 

 then is slow, four weeks at least being required for an 

 appreciable growth. Primary cultivations from the lesions 

 cannot be obtained on ordinary culture media but should 

 be made on (a) Dorset's egg medium, (b) glycerinated 

 potato in Roux's tubes (Fig. 10, p. 76), the bulb being filled 

 with 5 per cent, glycerin in physiological salt solution, 

 (c) glycerin brain agar, or (d) glycerinated serum (prefer- 

 ably dogs'). Cultures direct from the sputum may be 

 obtained after treatment of the sputum with antiformin 

 (p. 395). Dorset's egg medium is prepared thus : the 

 contents of four eggs are well beaten up, 25 c.c. of water 

 are added, and the mixture is strained through muslin. 

 The fluid is then tubed, and the tubes are heated in the 

 sloping position to 70 C. for four hours. At the time of 

 inoculation, a drop or two of sterile water should be added. 

 Brain agar is prepared by making a 3 per cent, nutrient 

 agar of + 20 reaction, adding an equal volume of pounded 

 ox-brain, and sufficient glycerin to make 5 per cent, in 

 the mixture, and sterilising. Egg broth is also a good 

 culture medium. 



After culture on these media for some generations, the 

 tubercle bacillus will develop on 5 per cent, glycerin agar 

 (reaction -f- 15 or 20) and in 5 per cent, glycerin broth 

 (veal is best) ; it will also grow, though very slowly, on 

 glycerin gelatin at 22 C. Gelatin and blood-serum are 

 not liquefied. On glycerin agar the growth forms a dry, 

 crinkled and wrinkled, cream-coloured or brownish- 

 yellow film, which has been well described as resembling 

 the patches of lichen met with on trees (Fig. 40). The 

 growth, however, varies considerably, both in colour and 

 in the amount of wrinkling, though retaining more or 

 less the characteristics just mentioned. In broth it forms 

 soft, cream-coloured, flaky masses, which increase slowly 



