SPIRILLUM OF ASIATIC CHOLERA. 383 



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 FrankeP 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 months, particularly 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'reg- 

 ular development in cultures so placed. 



1 Zeitsehrift fur HygieDe, Bd. ii. p. 521. 



