14 MASS. EXPERIMENT STATION BULLETIN 414 



Of the fecal bacteria, 93.2 percent were in the first group {Escherichia coli), 

 2.2 percent were in the fourth group {Aerobacter aerogenes), and 4.6 percent in the 

 other ten groups (coliform intermediates). Of the cultures from water, 60.5 

 percent were in the first group, 3.6 percent in the fourth group, and 35.9 percent 

 in the other ten groups. If the uric-acid test is ignored and the organisms are 

 grouped on the basis of their Imvic reactions, the result will be to combine group 

 IV with group V, and group VII with group X. On this basis, the percentages 

 of cultures in the E. coli group are unchanged. Among the fecal strains the per- 

 centage of A. aerogenes is slightly increased to 2.7 percent and that of intermed- 

 iates is reduced slightly to 4.1 percent. The percentage of A. aerogenes among the 

 cultures from water is increased from 3.6 to 6.7 percent and that of the inter- 

 mediates is correspondingly reduced to 32.8 percent. Most of the intermediates 

 among this lot of cultures are in the second group, for which the name "Citro- 

 bacter" has been proposed. The sanitary significance of this group and of the 

 other intermediates is a much debated subject, but they are not generally con- 

 sidered to be indicative of immediate fecal pollution. 



B. Water from Abandoned Wells 



A second study (5) was made to confirm the results from water testing. Seven 

 wells on farms long abandoned were selected for study as described earlier in 

 this bulletin. All were removed from any immediate possibility of sewage pollu- 

 tion, and all were so situated that a minimum of surface water could get into 

 them. 



Results of the bacteriological examination of water from these wells emphasized 

 the results reported abov-e. All of the wells would have been condemned by the 

 "Standard Methods" as unsatisfactory for drinking purposes; yet sanitary in- 

 spections failed to disclose any source of dangerous pollution. Over 50 percent 

 of the cultures isolated proved to be coliform intermediates. A strict interpre- 

 tation of the results according to the "Standard Methods" appeared to be un- 

 satisfactory, and yet there was no other accepted basis that could be used. 



C. Comparative Study of Presumptive Media 



The next logical step appeared to be a study of media that had been proposed 

 for use in the bacteriological testing of water. The purpose was to find a medium 

 or method that would indicate accurately and directly the sanitary significance 

 of the bacteria present in raw waters. In this study (6) the media employed 

 were brilliant green bile broth (7) and methylene blue erythrosine brom cresol 

 purple broth (8). The first will be designated as B. G. B. and the second as B. 

 C. P. "Standard Methods" lactose broth, designated as S. M., was employed for 

 comparison. All media were made and used as directed in "Standard Methods" 

 (9). These three media were employed in parallel in testing 76 samples of raw 

 water. 



The quantities of each water sample inoculated into each medium were 10, 1, 

 0.1, 0.01, and 0.001 ml. Five tubes of each quantity were inoculated, making 

 1,900 tubes of each medium for the 76 water samples. All tubes were examined 

 for gas production after 24 hours' incubation, and all negative tubes were incu- 

 bated an additional 24 hours and examined again. All positive gas tubes were 

 confirmed on Endo's medium with refermentation tests in S. M. lactose broth. 



A summary of the results is found in table 2. B. G. B. gave about the same 

 number of positive presumptive tests and a higher percentage of confirmations 



