34 ELEMENTS OF WATEE BACTERIOLOGY 



or with alkaline permanganate of potash followed by 

 sulphuric acid, dried by draining, and sterilized by 

 dry heat at 160 C. for at least i hour, or by steam at 

 115-120 for 15 minutes. If not to be used immediately 

 the neck and stopper should be protected against dust 

 or other contamination by wrapping with lead-foil. 

 For transportation the bottle should be enclosed in a 

 suitable case or box. 



The greatest care must be taken that the fingers do 

 not touch the inside of the neck of the bottle or the cone 

 of the stopper, as the water thereby would become 

 seriously contaminated and rendered unfit for examina- 

 tion. It is well known that bacteria are found abun- 

 dantly upon the skin, and Winslow (Winslow, 1903) 

 has shown that even B. coli is present upon the hands 

 in a considerable number of cases. 



In order to obtain a fair sample, great precautions 

 must be taken, and these will vary with the different 

 classes of waters to be examined and with local condi- 

 tions. If a sample is to be taken from a tap, the water 

 should be allowed to flow at least five minutes (if from 

 a tap in regular use) or for a longer period in case the 

 water has been standing in the house-service system. 

 In the small pipes, changes in bacterial content are 

 liable to occur, certain species dying and others mul- 

 tiplying. 



If a sample is to be taken from a pump similar pre- 

 cautions are necessary. The pump should be in con- 

 tinuous operation for 5 minutes at least, and preferably 

 for half an hour before the sample is taken, in order to 

 avoid excessively high numbers due to the growth of 



