22 MASS. EXPERIMENT STATION BULLETIN 315 



the>' were tested for their methyl red, Voges-Proskauer, sodium citrate, and 

 uric acid reactions. To date the cultures have shown a tendency to give variable 

 reactions to the Voges-Proskauer test. The reactions to the other tests have not 

 changed. This study is a part of the project on the biological studies of bacteria 

 of the Coli-Aerogenes group. 



The Bacteriostatic Action of Dyes with Gram Positive Cocci. (James E. Fuller 

 and Morrison Rcgcsa.) It is common practice to employ one or more dyes in a 

 presumptive medium for water analysis, to inhibit the growth of gram positive 

 bacteria which might interfere with the tests for the Coli-Aerogenes group. This 

 study was undertaken to determine the concentrations of gentian violet, crystal 

 violet, basic fuchsin, and acid fuchsin which would prevent the growth of gram 

 positive cocci (staphylococci, hemolytic and non-hemolytic streptococci, sar- 

 cinae, and micrococci). Basic fuchsin exerted the most pronounced bacteriostatic 

 effect, crystal violet and gentian violet following in the order named. Acid 

 fuchsin had little bacteriostatic effect under the conditions of the experiment. 

 Streptococci were more resistant to the dyes than were the other organisms 

 studied. Acid production by the various organisms was studied, and it appeared 

 that organisms which produced more acid were more resistant to the dyes em- 

 ployed. Excellent and extensive studies of bacteriostatic action of dyes have 

 been reported by Churchman and by St earn and St earn. The present stud)' was 

 carried out in more specific detail than their work. This was related to the project 

 on the biological studies of the Coli-Aerogenes group. 



The Indol Tolerance of the Coli-Aerogenes Group of Bacteria. (Ralph L. 

 France.) The results of this investigation indicated: (1) that the indol tolerance 

 of the various strains under investigation cannot be used as a basis for differen- 

 tiating the fecal forms from the non-fecal forms; (2) that a dilution of 1:2,000 of 

 indol inhibited the growth of all the strains studied; and (3) that there was a 

 greater variation in the indol tolerance of the non-fecal aerogenes strains than in 

 the fecal coli strains. 



A Study of the Voges-Proskauer Test. (Ralph L. France.) The results of this 

 investigation indicated: (1) that the Leifson's and O'Meara's reagents for in- 

 dicating the presence of acetyl-methyl-carbinol in liquid media were equally 

 satisfactory, and that both were more satisfactory than the Standard Methods 

 technique or Werkmann's modification of the technique; (2) that the majority 

 of strains of Bacterium aerogenes studied produced acetyl-methyl-carbinol in 

 24 hours' incubation at 37°C.;(3) that a single incubation period of four days 

 resulted in errors, due to the fact that some strains produce acetyl-methyl- 

 carbinol in one, two and three days, but give negative tests thereafter; and 

 (4) that the more accurate method of testing for acetyl-methyl-carbinol produc- 

 tion by members of the Coli-Aerogenes group is to set up sufficient tubes to make 

 the test on each of five successive days. 



A Comparative Study of Brilliant Green Bile Broth and Dominick-Lauter 

 Broth with the Standard Lactose Broth in Testing Raw Waters. (Ralph L. 

 France.) The results of this investigation indicated: (1) that the Dominick-Lauter 

 broth did not compare favorably with the brilliant green bile broth or the stand- 

 ard lactose broth when used as a presumptive medium; (2) that the brilliant green 

 bile broth was a more satisfactory presumptive medium than the standard 

 lactose broth; and (3) that the so-called "parallel-tubing" method of confirming 

 the lactose broth tubes by inoculation from them into brilliant green bile broth 



