BOUILLON OR NUTRIENT BROTH 89 



cover-slips it is well to heat them in water and then in 50 

 per cent, sulphuric acid. After rinsing in distilled water, 

 wash in alcohol and wipe with a clean cloth. These should 

 be kept in a clean, covered dish. 



SECTION VII 



PREPARATION OF CULTURE-MEDIA 



The culture-media are arranged according to the groups 

 of soil microorganisms. Since it is not possible to grow all 

 of the strains of bacteria in one group on the same medium, 

 several formulae are given. 



MEDIA FOR THE DETERMINATION OF THE NUMBER AND FOR 

 THE SEPARATION OF SOIL BACTERIA 



Medium i 



Bouillon or Nutrient Broth 



Peptone 10 gm. 



Liebig's meat extract 3 gm. 



Distilled water 1000 c.c. 



1. Add to i liter of distilled water 3 grams of meat 

 extract and 10 grams of peptone. 



2. Record the weight of vessel and contents. 



3. Heat not above 50 C. in steamer or double boiler until 

 extract and peptone are dissolved. 



4. Titrate and adjust reaction to i per cent, acid, with 

 phenolphthalein as an indicator (+i). 



5. Boil over the free flame for fifteen minutes. 



6. Restore the loss in weight with distilled water. 

 ' 7. Titrate again. 



