BACTERIA IN WATER 39 



Another series of observations revealed the same sort of 

 rapid increase of bacteria. On the date of collection the 

 micro-organisms per cc. in a deep-well water (in April) were 

 seven. After one day's standing at room temperature the 

 number had reached twenty-one per cc. After three days 

 under the same conditions it was 495,000 per cc. At blood- 

 heat the increase would, of course, be much greater, as a 

 higher temperature is more favourable to multiplication. 

 But this would depend upon the degree of impurity in the 

 water, a pure water decreasing in number 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. 



Furthermore, it is desirable to remember that organisms, 

 in an ordinary water, do not continue to increase indefinitely. 

 There is a limit to all things, even to numbers in bacte- 

 riology. Cramer, of Zurich, examined the water of the Lake 

 after it had been standing for different periods, with the 

 following results: 



Hours and Days of No. of Micro-organisms 



Examination. per cc. 1 



o hours 143 



24 " 12,457 



3 days 323,543 



8 " 233,452 



17 " 17,436 



70 " 2,500 



The writer's own experience is entirely in agreement with 

 this cessation of multiplication at or about the end of a week, 

 and the later decline. 



Method of Examination. At the outset of a systematic 

 study of a water it is well to observe its physical characters. 

 The colour, if any, should be noted. Suspended matter and 



1 The cubic centimetre (cc.) is a convenient standard of fluid measurement 

 constantly recurring in bacteriology. It is equal to 16-20 drops, and 28 cc. 

 equal one fluid ounce. 



