28 AMERICAN MINERAL WATERS. 



(2) Motility. Young agar, broth, or gelatin cultures should be examined. Abnor- 

 mal conditions may cause non-motility, but when rejuvenated motility may develop. 



(3) Non-liquefaction of gelatin. Gelatin cultures are allowed to stand one month, 

 if possible, before recording final results. B. colacx generally liquefies gelatin only 

 after several days' growth. 



(4) Fermentation of dextrose. Broth showing from 30 to 70 per cent gas, with a car- 

 bon dioxid ratio to hydrogen as 1 is to 2. Mixed cultures of B. coli and other organ- 

 isms may give wide variations in the volume and quality of gas produced, but in pure 

 cultures this organism usually gives fairly uniform results. 



(5) Coagulation of milk. With acid production this is essential, and usually occurs 

 within 48 hours at 37 C. Boiling may be necessary with certain strains to produce 

 curding. 



(6) Indol production. In nearly every instance the test is positive, varying from 

 a trace to marked reactions. 



(7) Nitrate reductions. Same as for indol. 



In addition to the recommendations of the committee, the follow- 

 ing test is made in this laboratory : 



Gram-stain. Negative for B. coli. Additional culture media used 

 consist of potato, bouillon, and slant agar. These are used in rou- 

 tine practice, but not considered essential. 



QUANTITIES OF WATER TESTED FOR B. COLI. 



For ordinary water use 10 cc, 5 cc, 1 cc, 0.1 cc, 0.01 cc, and 0.001 

 cc, quantities which are inoculated into the bile fermentation tubes. 

 Dextrose tubes may be used as duplicates. They may or may not 

 give higher results than the bile medium, perhaps depending on the 

 virility of the organisms. With water thought to be polluted, the 

 quantities used vary in tenfold ratio from 1 cc to 0.0001 cc or higher, 

 according to the probable degree of contamination. 



STREPTOCOCCI DETERMINATIONS. 



The physical character of the fermentation tubes is noted, and 

 smear preparations from each tube showing visible growth are made, 

 stained, and examined microscopically for the presence of strepto- 

 cocci. Only typical chains with unmistakable morphology are con- 

 sidered positive for streptococci. This test is considered valuable 

 in substantiating the results obtained from the test for B. coli as an 

 index of pollution. Water is never condemned on the streptococci 

 findings alone, these results being considered only in connection with 

 the number of B. coli present. 



INTERPRETATION OF RESULTS. 



In determining the purity of a drinking water all the available 

 information concerning its history should be taken into consideration. 

 When possible a chemical examination should be made to substan- 

 tiate conclusions based on the bacteriological findings, it is also 



