72 MEDIA AND THEIR PREPARATION 
Rice Milk (Besson). 
Milk. cece eet 150 gms 
Peptone broth. ............. 00. ce eee eee 50 gms. 
Powdered rice... 0. ee eee 100 gms. 
Distribute the mixture in Petri dishes 1-2 com. deep. Heat to 
115° C. for twenty minutes. The mixture solidifies and forms an 
opaque layer. 
Dialyzed Milk. Dialyzed milk may be prepared by the addition 
of .10 ¢.c. of hydrogen peroxide to 500 c.c. of milk. Two hours later 
hydrogen peroxide should be added again and after four to five hours 
the whole is dialyzed. The sugar content is reduced 50 per cent and 
the normal quantities of fat and proteins are preserved. The milk is 
diluted one-fifth. 
Milk Agar (Hastings, 1904). This medium is prepared by adding 
to ordinary nutrient agar, which has been melted and cooled to 50° C. 
10 per cent sterile skimmed milk. If the milk is added to the agar 
while hot, the casein will be precipitated in course flocculent masses. 
The medium is poured into sterile Petri dishes and after hardening is 
streaked with the cultures. After incubation, if proteolytic action 
is present, there will be a clear zone about the streak which will not 
change when treated with dilute acids. This distinguishes the acid 
formers from the proteolytic bacteria. 
BIBLIOGRAPHY 
Ayers, 8. H. 1918. Casein Media Adapted to the Bacterial Examination of 
Milk. Ann. Rept. Bureau of Anim. Ind., 1918, 225-235. 
BanzHar, HE. J. and Hirscuiprrer, L. J. 1914. Studies in Preparation of 
Diphtheria Toxin Media (Analysis of Nutrient Materials) Collected Studies, 
Bureau of Laboratories, City of New York, 8, 2238-225. 
Bartow, B. 1912. A Spoilage of Canned Corn Due to a Thermophilic 
Bacteria. Thesis for Master’s Degree, University of Illinois, June, 1913. 
Becker, W. C. 1916. The Necessity of a Standard Blood Agar Plate for 
the Determination of Hemolysis by Streptococci. Jour. Inf. Dis., 19, 
754-759. 
Benpicx, A. J. 1913. The Use of Calcium Carbonate in Solid Media for 
the Differentiation of Sugar Fermenting Bacteria, Especially of the Colon- 
typhoid Group. Trans. 15th Intern. Cong. Hygiene and Demography, 
Vol. IT, 40. 
Berry JANE. 1914-15. Studies on Laboratory Media. Collected Studies, 
Bureau of Laboratories, City of New York, 8, 288-293. 
