BACTERIA AND RURAL WATER SUPPLIES 11 



of the experiments indicated that these methods, if properly developed, might 

 be used to advantage in detecting the degree of acid production by coliform 

 bacteria, thus making it possible to grade organisms on the basis of acid produc- 

 tion. While neither of these methods appeared to be desirable for routine testing 

 of water, they probabh could be developed for differential study of coliform and 

 other bacteria. 



At this point it seemed logical to spend some time studying the effects of 

 environment on the bacteria themselves. The first of the environmental factors 

 studied was indol. The source of indol has already been explained, and so far 

 these studies had been concerned with indol production only as a means of 

 identifN-ing cultures. This study was concerned with the possible effect of indol 

 on the growth of coliform bacteria. 



As the colon bacillus multiplies in the human colon it is constantly in the 

 presence of substantial concentrations of indol which it and other intestinal 

 bacteria produce from waste residues of digested food. Consequently the colon 

 bacillus must be able to tolerate indol, which is known to retard or prevent growth 

 of some other species of bacteria. Since the aerogenes bacillus and many of the 

 coliform intermediates develop in soil and decaying plant residues on the ground, 

 they would not be in contact with much indol, if any, and conceivably might be 

 less able than the colon bacillus to tolerate the compound. This was the argu- 

 ment on which the study was based. 



Different concentrations of indol (G) were added to a fluid culture medium 

 and tubes of the medium were inoculated with a number of cultures each of the 

 colon bacillus, the aerogenes bacillus, and intermediates. After a suitable incuba- 

 tion period the amount of growth in the tubes was determined. It was observed 

 that the colon bacillus was somewhat more resistant to the indol than were other 

 coliform bacteria. The differences were not great enough, however, to make 

 possible the distinction between fecal and non-fecal coliform bacteria. 



Bile is another intestinal factor that might be expected to have some influence 

 on the growth and characteristics of intestinal bacteria as compared with non- 

 intestinal forms. Bile has been employed effectively in the isolation of typhoid- 

 fever bacteria from stools and blood of typhoid fever patients. Bile is also a 

 constituent of the B. G. B. medium employed in a study already described (C). 

 At least one investigator (see abstract H) has reported that in the small intestines 

 of humans he found aerogenes bacilli and in the colons of the same individuals 

 he found only colon bacilli. He offered the opinion that the aerogenes bacilli 

 had been changed into colon bacilli by the intestinal environment. 



In the study here reported (H) a number of cultures of aerogenes bacilli were 

 cultivated for a number of months in media containing bile and bile salts. The 

 cultures were examined by the Imvic tests before the experiment was begun and 

 from time to time as the experiment progressed. There was no change at any 

 time in the Imvic reactions of the cultures, which indicated that if the aerogenes 

 were changed to coli in the intestine, the change probably would not be due to 

 bile or bile salts alone. 



In the last study (J) of the series the effect of bacteriophage on colon and 

 aerogenes bacilli was investigated. From its derivation, the word "bacteriophage" 

 means something that will eat bacteria, and that is the definition of the agent. 

 It is not known just what a bacteriophage is. Some authorities claim that it is 

 just a chemical digesting agent, probably' an enzyme. Others insist that it is a 

 living thing that digests bacteria just as bacteria digest various food substances 

 that they live on. If the bacteriophage is a living thing, it is so small that it 



