3o8 SENESCENCE AND REJUVENESCENCE 



In the second paper he uses the temperature coefficient of the 

 length of Hf e of sea-urchin eggs at high temperatures as a basis for 

 his conclusions. To determine the temperature coefficient of length 

 of Hfe Loeb subjects lots of freshly fertilized eggs of sea-urchins to 

 different temperatures above that in which they normally develop, 

 and then, by removing portions of each lot at intervals to room 

 temperature and allowing them to develop, he finds the length of 

 time at the high temperature which is just necessary to prevent the 

 eggs from developing into normal swimming larvae. The ratio 

 of these times for different temperatures is the temperature coeffi- 

 cient. These experiments give a temperature coefficient of approxi- 

 mately i,ooo for io° C, i.e., it requires only about one-thousandth 

 as long at 30° as at 20° C. to injure the eggs so that they do not 

 produce normal larvae. The temperature coefficient of the length 

 of life of unfertilized eggs Loeb finds to be about the same. 



The temperature coefficient of embryonic development in the 

 sea-urchins is 2.86 for 10° C, which means that a rise in tempera- 

 ture of 10° increases the rate of development 2.86 times. This 

 is about the usual temperature coefficient of chemical reaction at 

 these temperatures. 



Loeb's argmnent is that if the processes which determine devel- 

 opment and those which determine length of life are identical, they 

 must have the same temperature coefficient, and since they do not, 

 he concludes that they must be different. Death is therefore not 

 the final result of development, but of specific processes quite dis- 

 tinct from the developmental processes. He also attempts to 

 account for the supposed large numbers of individuals in the animal 

 Kfe of cold waters on this basis; at 10°, for example, animals develop 

 about one-third as rapidly but Kve one thousand times as long as at 

 20°; therefore the number of individuals aKve at any given time 

 must be much greater at the lower than at the higher temperature. 



There are several objections to this hne of argument. In the 

 first place, the processes which immediately determine death may 

 be very different from those which underhe development, and still 

 death may be the result of the developmental processes, because 

 these bring the organism into a condition where the death changes 

 can occur. Loeb, himself, admits this when he says that the 



