Water and Ice 189 



We should not forget that contaminated 

 water always tends to purify itself in certain 

 ways when exposed to the air in large volumes, 

 as in lakes or running streams. Nor should 

 we lose sight of the fact that a moderate 

 amount of sewage, when poured into a large 

 volume of water, becomes so considerably 

 diluted, that its dangerous elements are much 

 less numerous in any given glass or volume 

 of water than in sewage itself. But such con- 

 siderations can afford but little real consola- 

 tion to those who find themselves forced to 

 drink sewage, even though it be very largely 

 diluted. The sewage may contain one hun- 

 dred thousand typhoid germs to one teacupful, 

 while the diluted mixture has in it not more 

 than one to the same volume. But it should 

 never be forgotten that the one germ is capa- 

 ble of multiplying in the human body to an 

 enormous extent, and for this reason, in the 

 living bacterial poison dilution is of much less 

 significance than in ordinary poisons which are 

 not alive and self-propagating. 



The fact is, that in view of all that we have 

 seen of the nature of bacteria and their dis- 



