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withdrawn to be reoxidized and thus made ready for use 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, 
