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^effects of temperature upon them. The influence of temperature 

 upon any one given chemicai reaction is alwavs the same, the 

 degree of acceleration which any one chemical reaction undergoes 

 when the temperature is raised 10 degrees is characteristic of, 

 and serves to identify, that reaction. Now the velocity of the 

 growth of a sea-urchin embyro or the division of a chemically, 

 or naturally, fertilized sea-urchin's egg is doubled by a rise of 

 10 degrees Centigrade in the temperature at which it occurs, 

 but the velocity with which a sea-urchin's egg dies, if its life is 

 not saved by fertilization, is multiplied no less than 500 times by 

 a similar rise in temperature. Unquestionably, therefore, the 

 processes which underlie growth are very essentially different from 

 those which underlie death. 



Incidentally it may be pointed out that these results throw 

 an interesting light upon an apparently wholly unconnected 

 phenomenon. It has always been a matter of surprise to Arctic 

 and Antarctic explorers to observe the density of the population 

 of the intensely cold waters of these regions. The water swarms 

 with minute organisms belonging to the lower forms of life, in 

 fact they are usually far more abundant than they are in tem- 

 perate seas. The reason for this phenomenon is now clear. 

 Although these organisms develop more slowly in the cold waters, 

 their lives are so enormously prolonged as to far more than make 

 up for the delay in their development. To prevent a misappre- 

 hension from arising in the minds of those who may not be 

 familiar with biology, I may mention here that greater cold 

 need not be expected to prolong our lives, because we are 

 possessed of a physiological mechanism which maintains our 

 blood at a very nearly constant temperature, so that the processes 

 which occur within our tissues occur at the same temperature 

 whether the climate to which we are exposed is a warm climate 

 or a cold one. But the lowly organisms which so thickly inhabit 

 the Arctic and Antarctic seas are "cold-blooded" animals, that is, 

 their tissues are very nearly of the same temperature as their 

 surroundings. 



We are thus led to conclude, as I have pointed out, that the 

 processes which underlie death are essentially different from those 

 which determine growth and the attainment of maturity. Since 

 they are so different it is at least possible that we may one day 

 be in a position to arrest the one, while leaving unaffected the 

 other, to prevent decay and death while maintaining the normal 

 processes of mature life. When we recall the astounding advance 

 in our knowledge and control of life which the last few years has 

 yielded, he would be a daring man indeed who would venture 

 to deny that we may yet, in the countless centuries of human 

 effort which lie unrevealed before us, remove from our world the 

 dread suspense and enter upon that supreme command of 

 Nature which is the command of our own fates. 



