532 



ON INCREASE IN SIZE 



[PT. Ill 



Fremiet showed for the segmentation of Ascaris, it lengthens a Httle 

 on the high-temperature side of that. The points are well described 

 by one of Janisch's catenary curves. The velocity of development, 

 i.e. the reciprocal of the development time, correspondingly rises to 

 a maximum at 28°, and has a sigmoid form on each side of this 

 maximum. This peaked curve, part of which, it should be remembered, 

 corresponds to the Krogh "straight-line", is identified by Janisch 

 with the peaked curve which Duclaux in 1899 pointed out would 

 be produced by the operation of two separate factors giving complex 

 exponential curves, i.e. differentially affected by temperature change. 

 This peaked curve could be either symmetrical or asymmetrical. 



160 

 140 

 120 



100 I 



80 Cl 

 60 

 40 

 20 



38° 36 34 32 30 28 28 24 22 20 13 16 14 12 10 8° 

 Temperature 



Fig. 86. 



Perhaps further work along these lines will lead to conclusions about 

 critical temperatures and controlling reactions which would support 

 those of Crozier. 



Janisch gave a full mathematical treatment of these questions, and 

 also reported an investigation of the effect of heat on the embryonic 

 development of the "Mediterranean flour-moth" Ephestia kuhniella 

 (see also Hase). The time/temperature relation here also can be 

 expressed by an equation of the form 



y 



2 



% 



where m and a are constants and y is the time taken to complete 

 a given amount of development at time x. Such presentations 



