CULTURE MEDIUM FOR TUBERCLE BACILLUS 413 

 PREPARATION OF THE MEDIUM 



1. Egg-white solution. This is made by diluting the egg- 

 white with ten parts of distilled water and thoroughly shaking. 

 The fluid is opalescent and contains numerous whitish flakes. 

 To clear it, it is passed through a thin layer of cotton and then 

 heated to 100°C. to hasten precipitation. It is then filtered 

 through paper. 



2. Egg-yolk solution. The yolks are diluted with ten parts 

 of water and well stirred. The very cloudy emulsion is clarified 

 by adding normal sodium hydroxid. Too much hydroxid is 

 harmful and therefore complete solution of the yolk is not de- 

 sirable. The emulsion should be slightly turbid. To attain 

 the proper degree of turbidity, one cubic centimeter of normal 

 sodium hydroxid is usually added to each one hundred cubic 

 centimeters of the emulsion. This is not a constant amount, 

 however, because some yolks wifl be completely dissolved by 

 less than half this amount of alkali. The solution is heated to 

 100°C. and filtered. 



3. Meat infusion. Five hundred grams of finely chopped 

 lean veal are covered with one Hter of water containing 15 per 

 cent of glycerin, allowed to infuse for twenty-four hours and 

 filtered; 5 grams of sodium chlorid are added, and the infusion 

 heated to boiHng. It is again filtered and then rendered plus 

 1 per cent alkaline. 



With the above solutions, the medium is made as foHows: 

 Place 300 cc. of the 10 per cent egg-white solution in a hter 

 flask; 300 cc. of the 10 per cent egg-yolk solution in another flask; 

 and 400 cc. of the meat infusion, to which is added 15 grams of 

 powdered agar-agar, in a third flask. These are then sterihzed 

 in the autoclave at 15 pounds pressure for fifteen minutes. They 

 are removed from the steriHzer and, while hot, 1 cc. of a 1 per 

 cent alcohohc solution of gentian violet is added to the broth- 

 agar. The contents of this flask are now poured into that con- 

 taining the egg-white and then the egg-yolk is added. The 

 whole is poured back and forth from this flask to another so 

 as to insure thorough mixing and then it is tubed and slanted. 



