Wells 93 



and prove convincingly that shallow wells situated near 

 cess-pools and privy-vaults should be regarded with 

 suspicion. Past freedom from disease germs can never 

 serve as a guarantee of future safety. It has been shown, 

 time and again, that such germs may ultimately find 

 their way into the well, and outbreaks of typhoid may 

 occur, not only on account of the direct use of the water, 

 but, also, on account of the use of such water in the 

 washing of milk cans and other dairy utensils. It happens 

 that milk is a good culture medium for typhoid bacilli. 

 A few drops of well-water containing a single typhoid 

 germ may be sufficient for the production of vast num- 

 bers. Some severe typhoid epidemics have been traced 

 directly to the consumption of infected milk. 



Deep wells and springs. — The thorough filtration of 

 the ground-water which finds its way into deep wells 

 makes it almost germ-free. Numerous examinations 

 of such waters have shown them to contain usually 

 less than 50 bacteria per cubic centimeter. At times the 

 number does not exceed 4 or 5 per cc, and it is very 

 seldom that as many as 100 or 150 per cc. are found. 

 This does not mean that deep-well-water is incapable 

 of supporting a vigorous growth of bacteria. On the 

 contrary, samples of deep-well-water, when allowed to 

 stand for a few days, frequently show an enormous 

 multiplication of their bacteria, while similar samples 

 of surface water containing a much larger number of 

 organisms, show a development decidedly more feeble. 

 The difference is probably due to the fact that 

 the organisms in the surface water suffer from com- 

 petition among themselves, and, likewise, from the 



