NUTRIENT GELATIN 91 



The hydrogen electrode may be used to determine the reaction of culture- 

 media. 



' Fuller, G. W., Jour, Pub. Health Assoc, vol. xx, pp. 381-399, 1895. 

 Standard Methods of Water Analysis, 1915. 

 Clark, W. M., Jour. Inf. Diseases, vol. xvii, pp, 109--136, 1915, 

 Anthony and Ekroth, Jour. Bact., vol. i, pp. 230-232, 1916. 

 Itano, A., Bui. 167, Mass. Agr. Exp. Sta., 1916. 



12. Titration of 5f{?//z.— Titrate the two samples of 

 broth prepared by the instructor. Determine the amount 

 of N/i alkali or acid required to make i Hter of these 

 solutions (+1). Do this for each sample. Titrate sample 

 No. 2, hot and cold, using phenolphthalein and litmus as 

 indicators. Record results. 



Medium 2 

 Nutrient Gelatin 



Gelatin 100 to 150 gm. 



Liebig's meat extract 3 gm. 



Peptone : 10 gm. 



Distilled water 1000 c.c. 



1. In a convenient vessel measure xooo c.c. of nutrient 

 broth. 



2. Add 10 per cent., on the dry basis, of gold label sheet 

 gelatin. Let the gelatin soak five to ten minutes. 



3. Heat over water-bath until dissolved. 



4. Adjust the reaction as directed in the preparation of 

 nutrient broth. Gelatin is decidedly acid and will require 

 more NaOH to neutralize it than bouillon or agar. 



5. Cool this mass to about 60^ C. Add the whites of 

 two eggs or 3 grams of powdered egg-albumen to 25 c.c. 

 of water. Stir into the gelatin and heat in a double boiler. 

 The egg-albumen will coagulate and inclose most of the 



