12 MASS. EXPERIMENT STATION BULLETIN 414 



cannot be seen through powerful laboratory microscopes, and it can pass through 

 fine filters that will not permit bacteria to pass through them. 



Bacteriophages have specific relationships, and a bacteriophage that will 

 digest one species of bacteria will not harm another. No bacteriophages have 

 been found for many species of bacteria, but they have been demonstrated for 

 those common in the intestinal tract. Bacteriophages can be isolated from 

 substances, water and sewage especially, that are heavily seeded with bacteria. 

 The kind of bacteriophage one can isolate depends upon the material and the 

 bacteria growing in it. Efforts have been made to purify water supplies by 

 inoculating them with a suitable bacteriophage. It has been demonstrated that 

 the agent can alter the characteristics of bacteria that are able to resist its di- 

 gesting action. 



In the study here reported (J) a coli bacteriophage was isolated from raw 

 sewage, and a culture of the colon bacillus was isolated from the same sewage. 

 Experiments proved that the bacteriophage would digest its related coli culture 

 isolated from the same sewage. Then other cultures of both colon and aero- 

 genes bacilli were placed, separately, in bottles of water (two liters each) and the 

 bacteriophage was added. The cultures were exposed thus to the action of the 

 bacteriophage for five months. 



Before the experiment was started, and from time to time for its duration, the 

 several types of bacteria were relsolated from the bottles of water and examined 

 by the several differential tests already described. No changes were noted in 

 either the appearance or the cultural characteristics of the bacteria employed, 

 except a slight change in their serological reactions which are too complicated 

 to explain here. One cannot conclude too much from experience with only one 

 bacteriophage, but the experiment indicated that If bacteriophage were present 

 in standing water, like that of the abandoned wells mentioned earlier (B), it 

 might destroy its related bacteria but it would not alter them into other forms. 



Concluding Comment 



To the reader it may seem that the experiments did not yield anything very- 

 definite, and in some respects that is true if each study is considered by itself. 

 However, the total result of the experience served to crystallize some ideas that 

 have been of substantial help In evaluating the methods employed and the results 

 obtained in testing raw water supplies from farms and other rural homes. 



The first two studies emphasized the importance of using care in interpreting 

 results of tests. The "Standard Methods" provide the only generally accepted 

 bacteriological procedure for the testing of water, and are designed primarily lor 

 use with public water supplies which usually are chlorinated at least, and which 

 often are sedimented and filtered. On the basis of experience and the experiments 

 reported, the conclusion was arrived at that the results of tests of untreated 

 private supplies must be interpreted liberally and emphasis must be placed on 

 the presence of the colon bacillus rather than on the aerogenes bacillus or inter- 

 mediates of the coliform group. It is desirable, where possible, to have a sanitary 

 survey of the source of water tested. 



The studies of the several media for the presumptive and confirmation tests 

 failed to find any substitutes for the media specified by "Standard Methods" 

 for these purposes. The studies with dissolved iron and precipitated erythrosin 

 indicated that the two procedures might be developed for certain differential 

 examinations of bacterial cultures, but there seemed to be no justification for 

 attempting to develop them into testing methods. Studies on the effect of bile, 



