DETERMINATION OF ORGANISMS 



71 



in midsummer bacteria capable of growth at 37 are 

 more abundant in normal waters than in winter and 

 spring. 



Winslow and Phelps examined 86 samples from 

 springs, wells, brooks and pools during the winter 

 and spring months and found only 12 which showed 

 more than 25 bacteria per c.c. and only 3 which showed 

 more than 100 per c.c. on lactose-agar. On the other 

 hand, of 58 samples from corresponding sources 

 examined in summer, 16 contained more than 100 

 bacteria per c.c. A series of 20 pools, ponds, and brooks 

 at Mt. Desert, Me., which were entirely free from 

 human or animal pollution, were examined in the late 

 summer of 1906. Only 4 of the 20 samples gave 



20 AND 37 COUNTS OF RAW WATER AT WILMINGTON 

 FILTER PLANT 



(WHIPPLE, 1913) 



