DISTRIBUTION AND HABITAT OF THE BACTERIA. 713 



the cultivation, which has heen able to exert a decided 

 influence on their multiplication and preservation. In 

 numerous experiments which have been made in the 

 author's laboratory multiplication of cholera bacilli has 

 never been observed in any water when only small 

 numbers of the organisms were sown ; on the contrary, 

 they have always died within eight to fourteen days. 



In these laboratory experiments the conditions are 

 particularly favourable for the development and preserva- 

 tion of the pathogenic bacteria, because sterilised water 

 has always been employed for the cultivation experi- 

 ments. Under ordinary circumstances the saprophytes, 

 which are always present in large numbers in water, 

 must render the conditions much more unfavourable 

 for the existence of the pathogenic bacteria. This has 

 in fact been directly proved by experiments made by 

 Wolffhiigel and Kiedel, who have found that cholera 

 bacilli disappear in unsterilised water even after two 

 days, although large quantities are introduced. 



The entrance of the bacteria into the water does not Mode of 

 occur to any great extent through layers of intact soil, bacteria 6 into 

 or through the ground water. The unanimous results wells - 

 of the experiments made by Koth,* Bolton,t Heraeus,J 

 and others show that in the majority of wells the number 

 of bacteria constantly decreases the more fresh ground 

 water is drawn into them by continuous pumping. 

 Further, after the pumping has been continued for some 

 time there are unusually few bacteria in the wells if they 

 are well covered on the surface and protected, as far as 

 possible, from fresh contamination from the well wall and 

 from the pumping tube; e.g., where we have tubular iron 

 wells and conducting pipes. Hence we must conclude 

 that the bacteria reach the drinking and household 

 water chiefly by currents from the surface, and also by 

 cracks and passages which run through the soil from 

 cesspools, &c., towards the wall of the well. It is 

 evident that pathogenic bacteria can also reach wells in 



* Viertelj.f. ger. med., N. F., Bd. 43, Heft 2. 

 t Zeitschriftf. Hygiene, Bd. 1, Heft 1. 

 J Ibid., Heft 2. 



