320 



THE TUBERCLE BACILLUS 



11. Potato. The tubercle bacillus will grow on ordinary potato but to 

 obtain the best results it is necessary to add glycerin (Nocard). 



Cut the potatoes into suitably-shaped pieces and leave them to soak in a 

 large quantity of a 15 per cent, solution of glycerin in water for two days in 

 the ice chest, then transfer them to a number of Roux's tubes and sterilize 

 in the ordinary way. 



On this medium growth appears about the twelfth day generally taking 

 the form of a thick, folded, soft layer, very occasionally it is dry and wrinkled. 

 The growth often extends in the form of a film over the liquid which has 

 drained away into the lower part of the tube. This film will be found very 

 useful for sowing liquid cultures. 



(a) 



llth Generation 

 70 days old. 



12th Generation 

 30 days old. 



FIG. 210. Cultures of tubercle bacilli of human origin on glycerin-potato, 

 (a) A bovine tubercle bacillus isolated from the meninges of a child aged 2 years 

 who died of tuberculous meningitis. The culture proved highly virulent for 

 the calf, rabbit, guinea-pig and cat. (6) An human tubercle bacillus isolated 

 from the sputum of a youth aged 16 years suffering from pulmonary tuber- 

 culosis. The culture grew luxuriantly on artificial media and was slightly 

 virulent for rabbits (A. S. Griffith). (See footnote p. 316.) 



Jurewitch recommends a potato broth. Leave a potato mash to macerat 

 in its own weight of water for a day, then filter through muslin and to the 

 filtrate add an equal volume of meat extract, 0*5 per cent, peptone (Chapo- 

 teaut), 0'5 per cent, salt and 3 per cent, glycerin : make distinctly alkaline 

 and complete the preparation as in making ordinary broth (p. 30). 



C. Differentiation of the various types of tubercle bacilli by cultural methods. 



[A. S. Griffith (for the English Commission) investigating the cultural 

 characters of mammalian bacilli, proceeds as follows. From the primary 

 culture on egg the bacillus is transferred to pure serum until it is growing 

 vigorously : it is then tested on the differential media. On these media human 

 tubercle bacilli produce luxuriant growths while bovine tubercle bacilli grow 

 much less luxuriantly. It is possible thus to determine the type of bacillus by 

 cultural characteristics alone. The differential media are serum, agar, potato 

 and broth, all containing glycerin. The serum, agar and broth contain 5 per 



