WATER AND SEWAGE 623 



were formerly regarded as safe waters; those containing from 100 to 

 500 organisms per cubic centimeter were regarded with suspicion, and 

 those containing 1000 or more organisms were pronounced dangerous 

 for domestic use. In the abstract these standards are fictitious; sur- 

 face waters even in uninhabited districts may contain many hundreds 

 of bacteria per cubic centimeter after rains, yet the bacterial count 

 would convey but little information of the actual sanitary status of 

 the water. Successive bacterial counts carried out over long periods 

 of time, on the other hand, are frequently of very great value. 1 



A direct examination of water for pathogenic bacteria, as the typhoid 

 bacillus, if it were practicable, would be a most satisfactory method of 

 evaluating domestic water supplies, for it is the presence of these 

 organisms harmful to man which, in the last analysis, makes water 

 containing them dangerous for human consumption. Unfortunately 

 it is not practicable, as numerous observers have amply demonstrated, 

 to isolate pathogenic organisms of this type directly from water, and 

 there are but few authentic records of a successful cultivation of the 

 typhoid bacillus from water supplies known to be infected, in spite 

 of numerous attempts. 



The practical impossibility of isolating pathogenic bacteria from 

 water has led to the development of methods for the detection of Bacil- 

 lus coli and organisms found practically constantly in human and 

 animal excrement. Bacillus coli is somewhat more tolerant of environ- 

 mental conditions as they exist in water than Bacillus typhosus, and 

 its constant presence in fecal discharges makes it somewhat more 

 effective as an indicator of excrementitious contamination than the 

 frankly pathogenic organisms. The simplest and in many respects 

 the best method for detecting Bacillus coli in water is to add graduated 

 amounts of the sample to be analyzed beginning with 1 c.c. and 

 decreasing the amount one-tenth in successive cultures to lactose 

 fermentation tubes. 2 A production of gas within twenty-four or 

 forty-eight hours is suggestive, but not conclusive evidence of the 

 presence of the organism. If gas develops some of the culture should 

 be placed on Endo medium, and red colonies that develop are tested 

 for their ability to produce acid and gas in dextrose and lactose media, 

 for indol production in sugar-free broth, for their action upon milk, 



1 For an excellent resume of the subject, see the Bacteriology of Surface Waters in 

 the Tropics, Clemesha, London and Calcutta, 1912, and Prescott and Winslow, Ele- 

 ments of Water Bacteriology, New York, 1913. 



2 Theobald Smith, Notes on Bacillus coli communis and Related Forms, Am. Jour. 

 Med. Sci., September, 1895, 283. 



