SURVIVAL OF PATHOGENS IN SOIL AND WATER 33 



tic relation appeared to exist in some soils but not in others and that this 

 was due to the action of specific antagonistic bacteria present in the par- 

 ticular soils. 



Frost (302) also reported that typhoid bacteria are rapidly destroyed 

 when added to the soil. In 6 days, 98 per cent of the cells were killed, 

 and in the course of a few more days all the cells tended to disappear 

 entirely from the soil. Under conditions less favorable to the growth of 

 antagonists, the typhoid organism survived not only for many days, but 

 even for months. The conclusion was reached that when soil bacteria are 

 given a chance to develop by-products, there results a marked destruc- 

 tion of typhoid organisms brought into contact with them. 



The survival of typhoid and dysentery bacteria in soil has been the 

 subject of many other investigations (256, 577, 685). 



Among the factors responsible for the disappearance of E. typhosa 

 in water, the presence of certain water bacteria was found to be of spe- 

 cial importance (899). Rochaix and Vieux (760) demonstrated that 

 when an achromogenic strain of Pseudomonas aeruginosa was present in 

 drinking water, it was not accompanied by any other bacteria. Media 

 inoculated with this organism and E. coU gave, after 13 days' incubation, 

 only cultures of the former. That the two organisms could coexist, how- 

 ever, was shown by inoculation into sterilized water. Only the actual 

 development of the antagonist led to the repression of the fecal organ- 

 ism. The oxygen supply of the water is important (975). E. tyfhosa 

 added to activated sludge increased within the first 4 to 6 hours ; this was 

 followed by a reduction in 24 hours, and a 99 per cent destruction in sev- 

 eral days (411). The survival period was shorter in sewage-polluted 

 than in unpolluted waters, especially when the sewage was aerated. 

 About 80 per cent reduction of typhoid bacteria was obtained in the 

 Netherlands East Indies by the passage of sewage through Imhoff 

 tanks. Digestion of sludge reduced the number further but did not 

 eliminate the bacteria completely j after the sludge was dried no typhoid 

 bacteria could be found (613). 



A study of microorganisms antagonistic to E. coli resulted in the iso- 

 lation of organisms from 5 of 44 samples of well water, i of 1 2 sam- 

 ples of spring water, and 6 of 1 6 samples of surface water. The antag- 

 onists included 3 strains of Pseudomonas, i each of Sarcina, Micro- 



