348 BACTERIOLOGY. 



are present, up to 20 C., the longer do they retain their 

 vitality ; the purer the water, that is, the poorer in 

 organic matters, the more quickly do the organisms die, 

 whereas the richer it is in organic matter the longer do 

 they retain their vitality. 



Still another point that must be considered in this 

 connection is the antagonistic influences under which 

 they find themselves when placed in water containing 

 large numbers of organisms that are, so to speak, at 

 home in water the so-called normal water bacteria. 



The effect of light upon growing bacteria must not 

 be lost sight of, for it has been shown that a surprisingly 

 large number of these organisms are robbed of their 

 vitality by a relatively short exposure to the rays of the 

 sun, and it is, therefore, not unlikely that the non- 

 observance of this fact may be, in part at least, account- 

 able for some of the discrepancies that appear in the 

 results of these experiments. 



In his studies upon the behavior of pathogenic and 

 other micro-organisms in the soil, Carl Frankel 1 found 

 that the cholera spirillum was not markedly susceptible 

 to those deleterious influences that cause the death of a 

 number of other pathogenic organisms. During the 

 months of August, September, and October, cultures 

 of the comma bacillus that had been buried in the 

 ground at a depth of three metres retained their 

 vitality ; on the other hand, in other mouths, particu- 

 larly from April to July, they lost their vitality when 

 buried to the depth of only two metres. At a depth 

 of one and a half metres vitality was not destroyed, 

 and there was a regular development in cultures so 

 placed. 



i Zeitschrift f. Hygiene, Bd. ii. p. 521. 



