70 Bacteria in Relation to Country Life 



In the first place, it may be considered that the 

 destruction of the intestinal bacteria is accomplished 

 by the formation by the other bacteria of substances 

 injurious to them. In other words, the growth of the 

 water and soil bacteria may lead to the formation of 

 substances toxic (poisonous) to the intestinal bacteria. 

 That the excreta or by-products actually formed by 

 bacteria or plants may actually prove poisonous to 

 themselves or to other organisms when accumulated 

 to a large extent, can be well illustrated. An instance 

 of this is the necessity of frequently supplying fresh 

 water to plants grown in water-culture, even when an 

 abundance of available plant-food exists. 



The other standpoint leads us to assume that the 

 intestinal bacteria are not destroyed by the poisonous 

 excreta of the others, but by actual contact. There is 

 some evidence to ihow that in case of the typhoid germs, 

 at least, the latter mode of action may serve as the de- 

 structive agents. But whether we regard the disappear- 

 ance of the intestinal bacteria in drinking-water from 

 one or the other standpoint, it remains certain that the 

 activities of the other organisms contribute largely to 

 their rapid disappearance. 



Numerous experiments carried out with cultures of 

 the typhoid germ prove conclusively that the organisms 

 survive for a longer time in sterilized than in unsterilized 

 water. It was shown, for instance, that typhoid germs 

 introduced into unsterilized water from Lake Michigan, 

 survived for only seven or eight days, whereas, in the 

 same water, previously sterilized, they remained alive 

 for twenty-five days, In other experiments, it wfig 



