BACTERIOLOGY. 151 



CHAPTER XXV. 



CULTIVATION AND SYSTEMATIC STUDY OF BACTERIA. 

 CULTIVATION OF BACTERIA. 



This is accomplished by the use of certain media upon which the 

 species to be cultivated will grow. Such are potato, blood serum, 

 gelatin, and agar-agar. The medium, when prepared, is placed in 

 cotton-stoppered tubes and then sterilized. In the case of gelatin 

 and agar-agar, a steam sterilizer can be used, and sterilization 

 should be made on three successive days, from fifteen minutes to 

 one hour each day. 



CULTURE MEDIA. 



The following formulas for the preparation of culture media will 

 be useful: 



1. Meat broth. To one liter of water add one pound of finely- 

 chopped lean meat,, free from all fat. Let stand over night, or heat 

 for one hour, but do not boil. Filter. 



2. Bouillon. To one liter of meat broth add ten grams of pep- 

 tone and five grams of sodium chloride. The peptone and sodium 

 chloride should be thoroughly mixed in a mortar with water, until 

 a thin paste is formed, before adding them to the meat broth. Cook 

 one hour, filter, and alkalize with a solution of sodium carbonate. 

 Sterilize. 



3. Agar-agar. To one liter of bouillon add fifteen grams of agar. 

 Cook in sterilizer, or double sauce-pan, until agar is dissolved, one 

 to three hours. Neutralize with solution of c. p. Na 2 Co 3 . Filter. 

 Cool to body temperature and add the whites of two eggs, which 

 have been previously mixed with 100 c. c. of water. Cook one hour. 

 Filter with coarse 'filter to remove coagulated albumen. Heat again 

 and filter with best filter paper previously moistened with boiling 

 water. Should any of the medium fail to filter through the first 

 paper, it should be heated again, and a second paper used for that 

 portion. Fill tubes and sterilize on three successive days. Cool 

 with tubes in oblique position. 



