METABOLISM 71 



hydrogen, about 250° below zero centi- 

 grade. At this temperature substances 

 which under ordinary conditions undergo 

 violent reactions with each other do not 

 show any activity when brought into 

 intimate contact. It is a temperature 

 at which all chemical reactions practi- 

 cally cease. If there is any chemical 

 activity in seeds at this temperature it 

 is certainly much less than exists in what 

 we call dead seeds at ordinary temper- 

 atm'e. Yet when these cooled seeds are 

 warmed up again and planted in moist 

 soil they grow and develop normally. 



We cannot say what would happen 

 if these seeds could be cooled down to 

 - 273° instead of to - 250° C. It does not 

 seem probable that this relatively small 

 difference in cooling would prevent them 

 from recovering. At —273° C (absolute 

 zero) all chemical processes would come 

 to a standstill and if we regard life as a 

 physicochemical process we should say 

 that it was extinct. 



We are led, therefore, to look upon 



