PRIVATE WATER SUPPLIES 7 



"determines whether or not the water contains typhoid or dysentery bac- 

 teria." For, and again some readers will be disappointed, even with these 

 chemical methods, no attempt is made to isolate disease-producing bac- 

 teria from the water. In other words, in the bacteriological test of water 

 no attempt is made by any method to determine whether ot not the water under 

 test contains typhoid or dysentery bacilli. The reasons for this are easily 

 understood. 



As explained above, the microscope is of little practical value in de- 

 termining tlie purity of water. To date bacteriologists have been unable to 

 devise a direct method that is both economically and technically satis- 

 factory for the isolation of disease-producing bacteria from water. As 

 stated above, there are normally present in water many other rod-shaped 

 bacteria which are harmless in so far as disease-producing capacities are 

 concerned, but which so closely resemble the typhoid bacilli in microscopic 

 appearance and in their "breathing" and "eating" habits that it is possible 

 to distinguish ainong them only by highly specialized methods. In a 

 routine water analysis such highly specialized methods are not desirable 

 froin an economic standpoint, if for no other reason. The disease-produc- 

 ing bacteria are for the most part rather "fussy" in their habits. The harm- 

 less bacteria on the other hand are more rugged, more vigorous, than the 

 disease-producers. One might say that these latter organisms are the 

 "aristocrats" of the bacterial world while the harmless ones are the 

 "peasants" or "workers." When mixed together the harmless bacteria 

 will outgrow and outlive the disease-producers. This is particularly true 

 in a medium such as water, where the food supply is generally very 

 limited. This is another reason why it is so difficult to isolate typhoid 

 and dysentery bacilli from a contaminated water. So, instead of using 

 a direct method for the isolation of disease-producing bacteria from water, 

 the bacteriologist makes use of an indirect method. 



There normally is present in the intestines of man and animals an or- 

 ganism known as "B. coli." This strain of bacteria is given off in the waste 

 materials in large numbers. The organism is harmless, and resembles 

 the typhoid and dysentery bacteria in that it is rod-shaped. It can be 

 rather easily identified by somewhat simple cultivation methods. The 

 presence of this organism in a water supply indicates that the supply 

 either is or has been receiving waste material of animal or human origin. 

 The numbers present will indicate to some degree the extent of contam- 

 ination. The argument presented when this test was devised was, of 

 course, that if "B. coli" could gain access to a water supply then typhoid or 

 dysentery bacteria might also gain access to the supply. Thus in the 

 •laboratory test this "B. coli" organism is used as an "indicator" of contam- 

 ination in water. This is what was meant when it was said that the 

 laboratory test was an indirect test rather than a direct test. 



So far it has been impossible to distinguish in the laboratory between 

 the "B. coW of human origin and that of animal origin, and there is little 

 reason to believe that such a distinction would have any practical value 

 in routine water testing. If either type is present in a water it means that 

 faulty construction or poor location is responsible. The mere presence 

 of "B. coli" in a water supply, be it of human or animal origin, indicates 

 that the water is unsatisfactory for drinking purposes. And, further, 

 drinking water containing waste material from any source is potentially 

 dangerous. 



