692 BACTERIA IN AIR, SOIL, WATER, AND MILK 



Examinations by various bacteriologists have shown that such wells 

 frequently contain as many as five hundred bacteria to the cubic centi- 

 meter. 



Perennial spring waters are usually pure. Examinations by the Mas- 

 sachusetts State Board of Health 1 in 1901 showed an average of about 

 forty bacteria per cubic centimeter. As sources of water supply for 

 general consumption, however, springs can hardly be very important 

 because of the insignificant quantities usually derived from them. 



Of much greater practical importance are deep artesian wells, which, 

 under ordinary conditions, are largely free from bacterial contami- 

 nation. 



Quantitative Estimations of Bacteria. The quantitative estima- 

 tion of bacteria in water is of necessity inexact, because of the difficulty 

 of always securing fair average samples from any large body of water, 

 and because of the large variations in cultural requirements of the 

 flora present in them. All these methods depend upon colony enumera- 

 tion in plates of agar or gelatin, preferably of both. For the sake of 

 gaining some basis of comparison for results which, at best, can never be 

 entirely accurate, an attempt has been made by the American Public 

 Health Association 2 to standardize the methods of analysis. 



Water for analysis should always be collected in clean, sterile bottles, 

 preferably holding more than 100 c.c. If water is to be taken from a 

 running faucet or a well supplied with piping, it is important that it 

 should be allowed to run for some time before the sample is taken, in 

 order that any change in bacterial content occurring inside of the pipes 

 may be excluded. It is obvious that in water pipes through which 

 the flow is not constant, bacteria may find favorable conditions for 

 growth and such a sample would not represent fairly the supply to be 

 tested. When the water is taken from a pond, lake, or cess-pool, the 

 bottle may be lowered into the water by means of a weight, or may be 

 plunged in with the hand, great care being exercised not to permit con- 

 tamination from the fingers to occur. 



After the water has been collected it is important te> plate it before 

 the bacteria in it haye a chance to increase. The changes taking place 

 during transportation, even when packing in ice has been resorted to, 

 have been found by Jordan and Irons 3 to be considerable. It is impera- 



1 Mass. State Bd. of Health, 33d Annual Report for 1901. 



2 Fuller, Trans. Amer. Public Health Assn., xxvii, 1902. Report of Com. on 

 Standard Methods of Water Analysis. Jour. Inf. Dis., Suppl. 1, 1905. 



3 Jordan and Irons, Reports of the Amer. Pub. Health Assn., xxv, 1889. 



