The Food Supply for Water Bacteria 67 



streams, lakes, and reservoirs, and the process of puri- 

 fication that occurs in filter beds are both connected 

 with the destruction or removal of the organic matter. 



On the other hand, the processes of purification that 

 depend upon the destruction of the bacteria themselves, 

 without the accompanying destruction of the organic 

 matter, are wholly inadequate. For instance, the bac- 

 teria in water could be killed by boiling, or by the addi- 

 tion of chloroform, yet after the water becomes cool 

 again, or after the chloroform evaporates, other bacteria 

 may gain access to the liquid, and, with the help of the 

 organic matter which the heat or the chloroform had 

 not destroyed, they may multiply as rapidly as ever. 

 The organic matter may be compared, in this case, to 

 a cask of gun-powder and the bacteria to a spark. While 

 the gun-powder is protected from the spark there is no 

 danger of explosion, yet great care must be exercised 

 to keep the two apart. Perfect safety can be assured 

 only by the removal or the destruction of the gun- 

 powder. 



The increase of bacteria in drinking-water, due to 

 the additions of organic matter, does not necessarily 

 involve also the increase of typhoid germs that m^y 

 find entrance to it. On the contrary, a large number of 

 investigations seem to indicate that the typhoid germs 

 and allied species' survive in water but a short time. 

 Furthermore, it actually appears that larger amounts 

 of organic matter in the water and the resulting active 

 multiplication of certain bacteria inhibit the growth 

 of typhoid germs to a greater extent than when the 

 amounts of organic matter are smaller. At the same 



