TESTS FOR BACILLUS COLI AS AN INDICATOR OF WATER POLLUTION [with DISCUSSION]

For nearly twenty-five years the number of colon bacilli present in water has been used as a test of its sanitary quality. The writer does not know who originally devised this test; but the first instance of its use with which he is familiar in this country is the study by Theobald Smith of certain New York river waters in 1893.1 The value of the colon test has been more and more generally recognized in this country and in England. In Germany there has always been a strong school which has been doubtful of its significance, but the more important recent papers, such as that of Quantz,2 recognize the value of the colon test if intelligently applied. The German investigators have performed a valuable service in emphasizing the fact that the number of colon bacilli present in a water is only one link in a chain of circumstantial evidence of which the sanitary inspection forms an essential and integral part. The writer is also wholly in accord with their contention that the 20° gelatin count is a test which is often of the greatest assistance in forming judgment of the quality of a water, having in mind for example the case of the water supply of Auburn, New York, Lake Owasco. In this lake, according to the exhaustive data collected by Mr. J. W. Ackerman the gelatin count rises sharply each year at the time of the spring thaw, while colon bacilli, never very abundant, are more numerous during the summer. The explanation of this phenomenon probably is that a certain proportion of colon bacilli are always contributed by the small brooks which enter the lake from agricultural land, which, not being of human origin, have but little significance. At the time of the spring thaws, which for the most part wash an open farming country, the normal contribution of B. coli from the fields is obscured by the rain and melting snow, while only the rise in total count