52 A CHEMICAL SIGN OF LIFE 



a very small amount of heat, or, indeed, they may 

 actually be heat-consuming rather than heat-producing. 

 And, indeed, if we had side by side reactions which pro- 

 duce and reactions which consume heat we might have a 

 considerable chemical change without the liberation of 

 much heat. Thus in a Daniels' cell there is a very 

 large transformation of energy with the liberation of 

 very little heat. The Weston cell has a still smaller 

 heat coefficient. The energy set free in the cell takes 

 the form of electrical energy rather than heat. To be 

 sure, it is ultimately converted into heat, but for the 

 time being it does not appear as such. There are many 

 chemical changes also which yield carbon dioxide and 

 yet liberate very little heat. It is possible that the 

 carbon dioxide is not produced by an oxidation, but by 

 a fermentative process which is hardly exothermic. 

 Many such hydrolyses liberate almost no heat at all. 

 We might have, for example, the oxidation going on at a 

 steady rate all the time, independently of the stimulus. 

 By this means a constant production of heat occurs, but 

 carbon dioxide is not liberated. That is, the change 

 has occurred at a steady rate in the oxygen atoms, which 

 is the essence of the oxidation. A very unstable com- 

 pound might result, awaiting only the hydrolysis of the 

 carbon dioxide. This last process might be that which 

 is accelerated by the stimulation and the passage of the 

 impulse. This liberates gas, but very little heat. The 

 reconstitution of the irritable substance might then be 

 brought about by a second molecule slipping in to take 

 the place of the first, while the exhausted molecule was 

 withdrawn to be reoxidized and thus made ready for use 

 again. This reoxidation perhaps goes on all the time, 



