472 JOHN F. NORTON AND MARY V. SAWYER 



Sicre (1909) and Porcher (1911) have studied the use of various 

 peptons finding that some akeady contain indol and that with 

 others indol is never produced by bacteria, so that it is necessary 

 not only to make blank tests on any chosen medium but also to 

 control experiments with a known indol-producing organism. 

 In each instance our tests were controlled by inoculating one tube 

 of medium with Bad. coli, an indol-forming organism, and 

 another with Bad. typhosum, a non-idol-former, and we regarded 

 such controls as essential. For media, besides Dunham's 

 pepton and the tryptophane medium of Zipfel, Rivas has suggested 

 trypsinized pepton (Rivas, 1912) and Cannon (1916), instead of 

 preparing pure tryptophane from casein as was done by Zipfel, 

 used hydrolyzed casein as the basis for his medium. 



Homer (1916) believes that tryptophane is necessary for bac- 

 terial life and if not present will be synthesized by the organisms. 

 Logic (1920) has used synthetic media containing ammonium 

 lactate with asparagin or sodium asparaginate and claims that 

 indol producing organisms possess an enzyme which enables them 

 to split off and utilize part of the tryptophane molecule. It is 

 possible that many organisms may be capable of synthesizing 

 indol but make use of it in their metabolism. 



For the hemophilic group a heated blood broth has been used 

 (Jordan, 1919). 



It is well known that the addition of glucose to a medium inter- 

 feres with the indol test. Fischer (1915) reports that lactose, 

 galactose, maltose or fructose are without effect. He believes 

 that this action of glucose is due not to acid production, as had 

 been supposed, but to the inactivation of the proteolytic enzyme 

 concerned in splitting the tryptophane. Logic (1920) found that 

 if glucose was added to a living culture of Bad. coli in which 

 indol had already been produced the latter rapidly disappeared. 

 From this he concluded that glucose caused an increased demand 

 in the organism for indol. Homer (1916) explains the effect 

 of the presence of glucose either on the basis of the preference of 

 the organism for glucose over tryptophane or by assuming the 

 formation of a chemical compound between glucose and trypto- 

 phane which is relatively stable. 



