214 CULTURE CHARACTERS 



Bact. tuberculosis does not grow upon the ordinary artificial 

 media, but may be grown upon human and beef blood serum, and 

 after it has been isolated for some time it may be grown upon bouil- 

 lon, agar and potato to which 5% of glycerine has been added. 

 Media which are suitable for the isolation of this organism and at 

 the same time are easy to prepare are Smith's dog blood serum 

 (Jour. Exp. Med., 1898, 3, 456), and Dorset's Egg Medium. The 

 last is the simpler, is very satisfactory, and is prepared as follows : 

 Perfectly fresh eggs are taken, shell broken at one end and the entire 

 contents poured into a wide mouthed sterile flask. The yolks are 

 broken with a sterile platinum wire and 25 cc. of water added to 

 each four eggs, and then the flask is shaken until the contents are 

 evenly mixed. The mixture is then strained through sterile cloth 

 which removes the bubbles and makes a homogeneous medium. Run 

 into sterile test-tubes, about 10 cc. in each, and incline in a serum 

 inspissator or oven and heat up to 70 C. until coagulated. This 

 usually requires four to five hours a day for two days. This is all 

 of the sterilization usually needed. If heated higher the medium 

 is hardened quicker but the tubercle germ does not seem to grow so 

 rapidly. Before inoculating the tubes they should be sealed and 

 placed in the incubator for several days. Cultures from tubercular 

 lesions are made by tearing the tubercle out with sterile forceps, 

 crushed as well as possible with the forceps, transferred to the egg- 

 slopes with a sterile platinum loop ; leave bits of tissue on medium, 

 avoid breaking surface of medium. (Amer. Med., 1902, and Bull. 

 52, Part I., Bureau of Animal Industry, 1904.) The tubercle bac- 

 terium is very sensitive to temperature variations and should there- 

 fore be kept at a temperature varying at most only a degree or two 

 from 38 C. It is also extremely sensitive towards desiccation, and, 

 for this reason, the cotton plug should be well paraffined, or replaced 

 by a cork through which a small cotton-plugged glass tube passes, 

 and the atmosphere of the incubator kept saturated with moisture. 



