166 MANUAL OF MICROBIOLOGICAL METHODS 



appearance of acid. It is often obscured by simultaneous digestion, how- 

 ever, and two other methods have been proposed which often show rennet 

 production with cultures that fail to show it when inoculated directly 

 into milk. 



Conn (1922) grows bacteria in milk sterilized in the usual manner; after the appear- 

 ance of whey or peptonized milk, 0.5 ml is transferred to 10 ml of unsterilized milk 

 and placed in a 37° incubator. Examinations are made every 5 min for the first half 

 hour and at less frequent periods thereafter for a few hours longer. First appearance 

 of coagulation is noted. Undoubtedly this test could be standardized, if desired, so 

 as to be performed like the other microtests given here. 



Gorini (1932) obtains vigorous growth on an agar slant, then covers the growth with 

 milk, fractionally sterilized at temperatures not over 100° so as not to alter the color of 

 the milk. The growth is mixed with the milk by use of a platinum needle, and the 

 tube is incubated at 37° until coagulation occurs. 



Although the committee is not prepared to recommend either method, 

 it is felt that by a combination of the two a good indication of rennet 

 production can be obtained. 



REFERENCES 



American Public Health Association. 1946. "Standard Methods for the Examina- 

 tion of Water and Sewage," 9th ed., published by the Association, New York. 



Arnold, W. M., Jr., and R. H. Weaver. 1948. Quick microtechniques for the identifi- 

 cation of cultures. I. Indole production. J. Lab. Clin. Med., 33, 1334-1337. 



Bachmann, Barbara, and R. H. Weaver. 1947. A quick microtechnique for the 

 detection of the reduction of nitrates to nitrites by bacteria. (Abstract) /. 

 BacterioL, 54, 28. 



Bartholomew, J. W., and W. W. Umbreit. 1944. Ribonucleic acid and the Gram 

 stain. J. BacterioL, 48, 567-578. 



Bisset, K. A. 1950. "The Cytology and Life-history of Bacteria." The Williams 

 & Wilkins Company, Baltimore. 



Bohme, A. 1905. Die Anwendung der Ehrlichschen Indolreaktion fiir bacterio- 

 logische Zwecke. Centr. Bakterioh, I Abt. Orig., 40, 129-133. 



Brough, F. K. 1950. A rapid microtechnique for the determination of nitrate reduc- 

 tion by microorganisms. /. BacterioL, 60, 365-366. 



Brown, H. C. 1922. Use of phenol red as an indicator for milk and sugar media. 

 Lancet, 202, 842. 



Clark, W. M., and H. A. Lubs. 1917. A substitute for litmus for use in milk cul- 

 tures. J. Agr. Hesearch, 10, 105-111. 



, and S. T. Cowan. 1952. Biochemical methods for bacteriology. /. Gen. 



MicrohioL, 6, 187-197. 



Clarke, P. H., and Cowan, S. T. 1953. Hydrogen siilphfde production by bacteria 

 /. Gen. MicrohioL, 8, 397-407. 



Coblentz, J. M. 1943. A rapid test for acetyl methyl carbinol production. Am. /. 

 Public Health, 33, 815. 



Conn, H. J., and G. J. Hucker. 1920. The use of agar slants in detecting fermen- 

 tation. /. BacterioL, 5, 433-435. 



' . 1922. A method of detecting rennet production by bacteria. /. Bac- 

 terioL, 7, 447-448. 



