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THE AMERICAN NATURALIST [Vol. XLII 



cerned with actual division ! Of course a motile flagellate 

 can not be followed and its life-cycle directly timed but 

 the information was obtained by estimating carefully 

 what percentage of individuals was in a state of actual 

 division at each temperature. It was found that always 

 4 per cent, were dividing, whatever the temperature. 

 This proves that the whole life-cycle is shortened in ex- 

 actly the same proportion as the process of division at 

 each temperature, and that it is just twenty-five times as 

 long. Therefore the life-cycle is 125 mins. at 35° C. 

 and 725 mins. at 15° C, so that here, again, we have 

 the physical-chemical relation with a factor of 2.4 for 

 each rise of 10° C. 



In this paper of Maltaux and Massart these relations 

 are not considered as the manifestations of physical-chem- 

 ical principles, but are regarded as reactions to stimuli; 

 and the paper contains a number of experiments upon the 

 effect of sudden changes of temperature upon the occur- 

 rence of division. As far as one can make out from in- 

 spection of the scattered literature, it does seem estab- 

 ished that sudden changes of temperature act as stimuli 

 in the strict sense of the word. In many investigations 

 one finds it stated that a quick change of temperature pro- 

 duced a certain reaction wliicii a -low rlinnuc of tempera- 

 ture failed to evoke. Usually all the phenomena are 

 treated in terms of stimulation, and the absence of reac- 

 tion with slow change of temperature is regarded as sec- 

 ondary. Were it not for the specific stimulatory effects 

 of quick change, which are not difficult to comprehend as a 

 phenomenon sui generis, 1 hardly think so general a tacit 

 acquiescence would have been extended by botanists to 

 the view that all enduring changes of velocity of metab- 

 bolism brought about by lasting changes of temperature 

 are stimulatory in nature. 



No determination of the rate of development of bacteria 

 through a very wide range of temperature seems to have 

 been made. There are various incidental experiments 

 which indicate values about 2 for the coefficient of in- 

 crease of metabolism for a rise of 10° C. 



