28o RALPH S. LILLIE. 



of a definite kind forms the determining condition of all. This 

 process is peculiar in undergoing marked acceleration by slight 

 rise of temperature ; it is also clear, from the fact that an effective 

 exposure must last for a certain minimal time at any temperature, 

 that the process must proceed to a definite stage before the egg 

 is rendered capable of continuing its development to advanced 

 stages; if the process is arrested before its completion, only the 

 earlier developmental changes can be carried out (membrane- 

 formation, early cleavage or change of form) ; if, on the other 

 hand, it is allowed to proceed too far, injurious conditions arise 

 which eventually prevent all development; a sufficiently pro- 

 longed exposure to high temperature renders the egg incapable 

 even of membrane-formation. 



In endeavoring to form some consistent conception of the 

 nature of this process the following facts have to be considered. 

 It exhibits a high temperature-coefficient: from fifteen to twenty 

 times the duration of exposure is required to induce membrane- 

 formation at 30° as at 35°; the ratios between 29° and 34° and 

 between 31° and 36° are the same. At each temperature the 

 proportionate durations of the minimum, optimum, and maxi- 

 mum exposures for forming larvae are approximately the same. 

 In other words, the critical change underlying simple membrane- 

 formation is affected by temperature in the same way as that 

 underlying complete activation of development: i. e., the pro- 

 portionate increase in velocity by rise of temperature is the same 

 in both cases, a fact which can only indicate that one funda- 

 mental process — and not two — is concerned in producing both 

 effects. If we assume that the above proportionate increase in 

 velocity prevails through a rise of 10°, a Qio value of from 225 to 

 400 is indicated, as against the 2 to 3 characteristic of chemical 

 reactions in homogeneous media.^ Activation by heat thus 



1 The temperature-coefificients of the rate of cj-tolysis of sea-urchin eggs and of 

 the duration of life of sea-urchin larvae and of Tubularia stems at temperature of 

 25° to 40° show similarly high values. In these cases the direct effect produced on 

 the cell by the high temperature is probably of the same kind as that underlying 

 the above activation-effect; this appears to be a change in the colloids of the plasma- 

 membranes, leading to an increase of permeability. (See below, p. 296.) Such 

 a change if not reversed within a certain time results in cytolysis. In the unfer- 

 tilized starfish egg temporary increase of permeability involves activation. For 

 data on the temperature-coefificients of cytolysis and heat-death, cf. J. Loeb, 



