MICROSPIRA COMMA. 473 



The results of experiments having for their object 

 the determination of the length of time during which 

 this organism may retain its vitality in water are con- 

 spicuous for their irregularity. 



Koch states that in ordinary spring-water or well- 

 water the organisms retained their vitality for thirty 

 days, whereas in the sewage of Berlin they died after 

 six or seven days ; but if this latter were mixed with 

 faecal matters, the organisms retained their vitality for 

 but twenty-seven hours ; and in the undiluted contents 

 of cesspools it was impossible to demonstate them after 

 twelve hours. In the experiments of Nicati and Rietsch 

 they retained their vitality in Marseilles sewage for 

 thirty-eight days; in sea- water, sixty-four days; in 

 harbor- water, eighty-one days; and in bilge- water, 

 thirty-two days.- 



In one test with the water-supply of Berlin the 

 organism retained its vitality for 267 days, and in 

 another for 382 days, notwithstanding the fact that 

 many other organisms were present at the same time. 

 There is no ready explanation for these variations, for 

 they depend apparently upon a number of factors which 

 may act singly or together. For example, in general it 

 may be said that the higher the temperature of the water 

 in which these organisms 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. 



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 vital- 

 ity by a relatively short exposure to the direct rays of 



