Journal of Applied Microscopy. 305 



DISCUSSION. 



Notes on Part V of Dr. Novy's Article on Laboratory Methods 



in Bacteriology. 



The writer has followed, with interest, the articles of Dr. F. G. Novy on 

 " Laboratory Methods in Bacteriology" in the Journal of Applied Microscopy, 

 but feels compelled to say that the methods for the preparation of culture media, 

 as used in the Hygienic Laboratory of the University of Michigan, and de- 

 scribed in Part V of Dr. Novy's article, are not based altogether on the modern 

 theor}^ of indicators or on the results of the latest investigations. 



The writer feels compelled to take exception to Dr. Novy's method for the 

 adjusting of the reaction of media and to his position with reference to the 

 superiority of litmus over phenolphtalein as an indicator for use io this con- 

 nection. Dr. Novy's method of titration uses up OOcc. of medium to determine 

 the reaction of the same, and he claims no greater accuracy for it than may be 

 easily obtained by Fuller's method (Journ. Am. Pub. Health Assn., Oct., 1895, 

 p. 381) using only 15cc. 



While criticising Dr. Novy's article, the writer has refrained from describing 

 methods differing from his because those which the writer has accepted, in com- 

 mon with many others, as the most advisable have been published in the Report 

 of the Bacteriological Committee (Journ. Am. Pub. Health Assn., January, 1808), 

 which report was the result of joint labors of the following gentlemen : J. G. 

 Adami, W. T. Sedgwick, G. W. Fuller, Charles Smart, A. C. Abbott, C. A. 

 Cheesman, Theobald Smith, and Wm. H. Welch. 



Dr. Novy cites the same objections against the use of phenolphthalein that 

 Dahmen did (Centralblatt, Bd. XH, p. 260) in 1892. These objections are 

 based on the presence in the media of ammonia salts and carbonates which may 

 interfere with the use of phenolphthalein ; they really do exist, but may be 

 readily overcome. The amount of ammonia at the time the reaction is usually 

 determined has been found to be less than one-tenth of the amount which inter- 

 feres with the accuracy of this indicator, and the error due to carbon dioxid is 

 obviated if the Bacteriological Committee's directions are followed. Phenol- 

 phthalein takes into account the bodies which have an amphoteric reaction to 

 litmus, but in which the acid character nevertheless predominates. These bodies 

 affect the growth of bacteria, while phenolphtalein is unaffected by phosphates 

 which have no effect on the growth of bacteria. 



Phenolphtalein contrasts very favorably with litmus in that the latter does 

 not react with those bodies which affect bacterial growth, and, on the other hand, 

 does react with phosphates which have no such effect on bacterial growth 

 (Fuller). Phenolphtalein therefore permits the preparation of media which yield 

 more uniform conditions of growth and thus makes quantitative bacteriological 

 analyses more definite and reliable. 



Dr. Novy seems to object to phenolphtalein because it gives a different end- 

 point from that obtained with litmus. As far as the writer knows, no one has 



