82 SA CTEBIOLOG Y. 



results quite satisfactory in their nature may be obtained 

 by the employment of the saturated sodium carbonate 

 solution for neutralization and litmus paper as the indi- 

 cator. For some time, however, it has been our practice 

 to employ the yellow curcuma paper for the detection of 

 alkalinity, rather than the red litmus paper. 



In the exhaustive paper of Fuller^ on this point it 

 was shown that the results obtained by titrating the 

 same culture medium with the same alkali solution 

 differed very markedly with the indicator employed. 

 For instance, a litre of ordinary meat-infusion nutrient 

 agar-agar required 47 c.c. of a normal caustic alkali 

 solution to neutralize it when pheuolphtalein was the 

 indicator used, 28 c.c. when blue litmus was employed, 

 and 5 c.c. when rosolic acid was substituted. It is 

 manifest from this that the actual reactions of media, 

 in the neutralization of which different indicators have 

 been used, may differ very widely from one another, 

 and that the results of cultivation on a medium neu- 

 tralized by one method are not fairly comparable with 

 those obtained when another indicator has been used. 

 For the sake of uniformity Fuller suggests that bacte- 

 riologists should agree upon some one trustworthy 

 method of neutralization and employ it to the exclusion 

 of other methods. He recommends, as the procedure 

 that has given the most satisfactory results in his hands, 

 a modification of Schultz's method, viz., 5 c.c. of the 

 culture medium are to be mixed with 45 c.c. of distilled 

 water in a porcelain evaporating dish and boiled for 

 three minutes, after which 1 c.c. of pheuolphtalein 



1 Fuller : On the Proper Reaction of Nutrient Media for Bacterial Cultiva- 

 tion. "Public Health " (Journal of the American Public Health Association), 

 Quarterly Series, 1895, vol. i. p. 381. 



