WATER ANALYSIS. 61 



WATER ANALYSIS. 



For public health purposes a bacteriological exami- 

 nation of water calls for an answer to the questions, (a) 

 are any pathogenic bacteria present ; (b) has the water 

 been polluted with sewage ; (c) are there many bacteria 

 present apart from sewage forms, and if so whence are 

 they derived. Practically the first and second questions 

 have to be considered together, for water-borne diseases 

 are primarily sewage-borne diseases. The third question 

 seldom assumes much importance from a purely public 

 health view point. Many bacteria are present in water, 

 laden with vegetable organic matter, and this class of 

 'water would afford the basis for most examinations in 

 answer to question (c). 



Care should be exercised in the collection of the 

 sample, so as to obtain a spBcimen which will give 

 the general biological characters of a water. For 

 this reason the water should be collected in cleansed 

 sterilized jars, bottles or flasks, stoppered with a 

 closely fitting cork. The samples should be sent 

 at once for analysis, as even several hours in warm 

 weather may change, to a considerable extent, the bac- 

 terial content of the water. If -there is any delay before 

 an analysis can be made, the sample should be carefully 

 packed in ice. 



Methods of Examination. 



For measuring exact quantities of water a pipette 

 graduated to .1 cc. is necessary. This should be prev- 

 iously sterilized, a small cotton plug being pushed in at 



