36 Elements of Water Bacteriology. 



increase is notably greater in bottles of the more soluble 

 glasses. 



Whipple's tables, quoted above, show that the multi- 

 plication during storage was greater at a higher temper-, 

 ature; and this is a well recognized general rule. In 

 order to obviate the abnormal results of storage increase 

 it is therefore obvious that samples must be examined 

 shortly after collection, and that they must be kept cool 

 during their necessary storage. If. fairly pure waters 

 are placed upon ice and kept between o degrees and lo 

 degrees, they will show no material increase in twelve 

 hours. With polluted water, however, another danger 

 is here introduced. Samples of such water when packed 

 ia ice show a marked decrease due to the large number 

 of sensitive intestinal bacteria present. Jordan (Jordan, 

 1900) found that three samples of river-water packed in 

 ice for forty-eight hours fell off from 535,000 to 54,500; 

 from 412,000 to 50,500, and from 329,000. to 73,000, 

 respectively. It is, therefore, important that even iced 

 samples should not be kept too long; and it is desirable 

 to adhere strictly to the recommendations of the Standard 

 Methods Committee that the interval between sampling 

 and examination should not exceed twelve hours in the 

 case of relatively pure waters, six hours in the case of 

 relatively impure waters, and one hour in the case 

 of sewage. 



Plating. — The bottle containing the sample of water 

 is first shaken at least twenty-five times in order to get an 



