722 



Tuberculosis 



guinea-pig are not crushed or comminuted, but are simply 

 laid upon the undisturbed surface of the blood-serum and 

 then incubated for several weeks. If no growth is apparent 

 after this period, the bit of tissue is stirred about a little 

 and the tube returned to the incubator, where growth al- 

 most immediately begins from bacilli scattered over the 

 surface as the bit of tissue was moved. As the appropriate 

 media, blood-serum was recommended by Koch; glycerin 

 agar-agar, by Roux and Nocard; glycerinized potato, by 



Nocard; coagulated dogs' blood- 

 serum, by Smith, or coagulated 

 egg, by Dorset, may be men- 

 tioned. The most certain results 

 seem to follow the employment 

 of the dogs' serum and egg media. 

 Cultivation. Blood-serum. 

 Koch first achieved artificial cul- 

 tivation of the tubercle bacillus 

 upon blood-serum, upon which 

 the bacilli are first apparent to 

 the naked eye in about two 

 weeks, in the form of small, dry, 

 whitish flakes, not unlike frag- 

 ments of chalk. These slowly 

 increase in size at the edges, and 

 gradually form small scale-like 

 masses, which under the micro- 

 scope are found to consist of tan- 

 gled masses of bacilli, many of 

 which are in a condition of invo- 

 lution. The medium is so ill 

 adapted to the requirements of 

 the tubercle bacillus and gives 

 such uncertain results that it is no longer used. 



Glycerin Agar-agar. In 1887 Nocard and Roux* gave a 

 great impetus to investigations upon tuberculosis by the dis- 

 covery that the addition of from 4 to 8 per cent, of glycerin 

 to bouillon and agar-agar made them suitable for the devel- 

 opment of the bacillus, and that a much more luxuriant de- 

 velopment could be obtained upon such media than upon 

 blood-serum. The growth upon "glycerin agar-agar" re- 

 sembles that upon blood-serum. A critical study of the 

 * "Ann. de 1'Inst. Pasteur," 1887, No. i. 



Fig. 239. Bacillus tuber- 

 culosis on "glycerin agar- 

 agar." 



