MULTIPLICATION OF WATER BACTERIA 35 



increase of bacteria. On the date of collection the micro-organisms 

 per e.c. in a deep-well water (in April) were seven. After one day's 

 standing' at room temperature the number had reached twenty-one 

 per c.c. After three days under the same conditions it was 495,000 

 per c.c. At blood-heat the increase would, of course, be much greater, 

 as a higher temperature is more favourable to multiphcation. But 

 this would depend in part also upon the degree of impurity in the 

 water, a pure water decreasing in number of germs on account of the 

 exhaustion of the pabulum, whereas, for the first few days at all 

 events, an organically polluted water would show an enormous 

 increase in bacteria. 



It is desirable to remember that organisms, in an ordinary water, 

 do not continue to increase indefinitely. Cramer, of Zurich, examined 

 the water of the Lake after it had been standing in a vessel for 

 different periods, with the following results: — 



In a general way it inay be said that foul waters, rich in putrescible 

 animal matter, show a rapid increase of bacteria ; surface waters, such 

 as river water, show a slow and persistent multiplication of organisms ; 

 and deep-well waters and spring water show comparatively little 

 increase in contained bacteria. Indeed it may be said that the 

 condition of a water is partly indicated by the rapidity or slowness 

 with which its bacteria increase. A low temperature (5° C.) 

 undoubtedly diminishes the multiplication, and there are other 

 conditions such as exposure to air,- movement, and antagonism of 

 organisms which exert an indirect effect. As will be inferred from 

 what has been said, the most important condition affecting the 

 number of bacteria in a water is the organic matter contained in it.* 



The Bacteriology of Water 



In many natural waters there will be found varied contents even 

 in regard to flora alone: algce, diatoms, spirogyra, desmids, and all 



* For suggestions and hints on points of technique in the systematic examination 

 of a water, see DeWpine's Bacteriological Survey of Surface Water Supplies : Jour, of 

 State Medicine, 1898, vol. vi., pp. 145, 193, 241, 289 ; and Bacteriological Examina- 

 tion of Water, by W. H. Horrocks. (See also present volume, pp. 463-473.) 



