344 WATER BACTERIOLOGY 



Before exposure. Sunshine. Darkness. 



At surface of water (per c.c.) . . 2100 9 3103 



Under 20 inches of water (per c.c.) 2103 10 3021 



Under 40 inches of water (per c.c.) 2140 2115 :;463 



Few studies have been made of the effect of light on bacteria in 

 flowing water. Jordan, after an investigation of several Illinois 

 streams, concluded that at least in eight moderately turbid waters 

 the sun's rays are virtually without action. Much, therefore, 

 depends on the turbidity and speed of the current, the maximum 

 germicidal effect being produced in shallow, clear, slow-moving 

 water. 



Temperature. The action of temperature upon the bacteria varies 

 with the food and specific organism. When they are in a medium 

 in which they can grow and multiply, warmth within reasonable 

 limits favors their development. This is true of the natural bac- 

 terial flora and may, as was found to be the case at Harrisburg, 

 Pennsylvania, hold for B. coli. But this does not hold for the 

 pathogens which in the majority of cases do not multiply in water, 

 and, as pointed out by Prescott and Winslow, "when a bacterium 

 cannot multiply, the only vital activity which can take place is 

 a katabolic wasting away, which soon proves destructive, and the 

 higher the temperature the more rapidly the fatal result is reached. 

 A frog in winter lives at the bottom of a pond breathing only 

 through its skin and eating not at all, but as soon as the temperature 

 rises it must eat and breath through its lungs or perish." The 

 typhoid bacilli will survive longer in ice than in water. The 

 speed with which they perish varies inversely with the temperature, 

 as was found by Houston. 



Percentage of typhoid Period of final 



bacilli surviving disappearance of 



Temperature. after one week. bacilli, weeks. 



46.00 9 



5 14.00 7 



10 0.07 5 



18 0.04 4 



In the natural-occurring waters probably many factors play a 

 part; sometimes it is the inhibiting action of microorganisms and 

 their products on one another; at other times protozoa which feed 

 upon bacteria and the development of which is directly proportional 

 to the temperature of the medium in which they are growing. 



Hinds found that in pure, natural and distilled water B. coli 

 and B. typhosus die from starvation at a regular rate. The rate 

 of death increases with the temperature and is similar to the rate 

 of a chemical reaction, thus following the mono-molecular law. 



Food. Bacteria are dependent upon food and respond quickly 

 to comparatively slight changes in their food supply. Wheeler 

 found that typhoid bacilli would persist in almost undiminished 



