444 BACTERIA PATHOGENIC TO MAN 



first run off, for otherwise the effect of metallic substances will invalidate 

 the results; if from lake or pond, the surface scum or bottom mud 

 must be avoided, but may be examined separately. The utensils by 

 which the water is taken should be of a good quality of glass, clean 

 and sterile. From a brook the water can be taken directly into a 

 bottle, the stopper being removed while it fills ; from a river or pond it 

 can be taken from the bow of a small boat, the bottle being held inverted 

 on a pole with a clamp until it has entered the water; from a well a 

 special apparatus has been devised by Dr. A. C. Abbott, where a bottle 

 with a leaded bottom is so held that when lowered to the proper 

 depth a jerk will remove the cork and allow the bottle to fill. The 

 same device can be rigged up readily by anyone. The sample of water 

 should be tested as soon as possible, for the bacteria immediately begin 

 to increase or decrease. In small bottles removed from the light preda- 

 tory micro-organisms and many bacteria begin to increase, and among 

 these are the members of the colon group. Thus, the Franklarids record 

 a case in which in a sample of well-water kept during three days the 

 bacteria increased from 7 to 495,000; while Jordan found that in a 

 sample the bacteria in forty-eight hours fell from 535,000 to 54,500. 

 In a sample I took from the Croton River the colon bacilli during twenty- 

 four hours increased from 10 to 100 per c.c. The only safe way to 

 prevent this increase is to plate and plant the water in fermentative 

 tubes within the space of one or two hours. It is far better to make 

 the cultures in the open field or in a house rather than to wait six to 

 twelve hours for the conveniences and advantages of the laboratory. 

 If sent to the laboratory, water should be kept below 40 C. 



The third matter of great importance is the adding of proper amounts 

 of water to the broth in the fermentation tubes and the media for plating. 

 Usually 1 c.c., 0.1 c.c., and 0.01 c.c. are added to the fermentation 

 tubes and to 10 c.c. of the melted nutrient agar or gelatin. If 

 possible duplicate tests should always be made. When it is desired 

 to know whether colon bacilli are present in larger amounts than 1 c.c., 

 quantities as great as 10 or 100 c.c. can be added to bouillon, and then 

 after a few hours 1 c.c. added to fermentation tubes. Less than ten 

 colonies and more than two hundred on a plate give inaccurate counts, 

 the smaller number being too few to judge an average and the larger 

 number interfering with each other. 



The chemical composition of the medium on which the bacteria are 

 grown affects the results of the analysis. Nutrient 1 per cent, agar 

 gives slightly lower counts than gelatin, but on account of its con- 

 venience in summer and its greater uniformity it is being more and 

 more generally used for routine quantitative work. There is an opti- 

 mum reaction for every variety of bacteria, and to ensure uniformity 

 the committee of the American Public Health Association in 1897 

 adopted a standard which was as near as possible to the average opti- 

 mum for water bacteria. Such a uniform standard is a necessity to 

 secure comparability of the results of various observers. At best only 

 a certain proportion of bacteria develop, and it is only important that 



