CHAPTER IV 

 THE ENERGETIC BASIS OF THE BODY 



SECTION I 

 THE ENERGY OF MOLECULES IN SOLUTION 



EVERY vital act involves at the same time a transformation of the 

 material basis of the living cell and a transformation of energy. The 

 ultimate source of the energies displayed by the animal organism is to 

 be sought in the chemical energy of the substances taken in as food. 

 In all the changes undergone by either matter or energy in the body 

 there is neither destruction nor creation. The living organism may 

 therefore be regarded in one sense as a machine, that is to say, a 

 system for the conversion of one form of energy into another. Thus 

 the steam-engine converts the potential energy of overheated steam 

 into mechanical work ; a gas-engine the chemical energy of an explo- 

 sive mixture of gases into heat and mechanical energy ; in a battery 

 there is a transformation of chemical into electrical energy ; in a 

 dynamo, of mechanical into electrical energy, and so on. In the living 

 cell the chemical energy of the food may undergo conversion into 

 any of the other forms mentioned above, i.e. heat, work, electrical 

 difference of potential, or it may be used for the production of 

 other chemical substances possessing perhaps as much potential 

 energy as or more than the food-stuffs themselves. 



The protoplasm, which is the seat of all these changes in both 

 plants and animals, is active only within fairly narrow limits of tem- 

 perature, approximately between 5 and 40 C. In consistence it is 

 slimy and wet, water forming from 70 to 95 per cent, of its bulk. 

 No substance introduced into the protoplasm has any influence on it, 

 unless it be soluble, and the first stage in the preparation of food-stuffs 

 for assimilation always consists in a process of solution. The sole 

 source of energy to the body being that conveyed with the food, it 

 follows that all the energy with which we have to deal is the energy 

 of molecules in watery solution, the playground of whose activities is 

 a jelly-like mass of colloidal material, heterogeneous yet structurally 

 continuous. It is important, therefore, at the outset to inquire into 

 the nature of this energy and the methods by which it may be measured. 



136 



