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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 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 



:~~achine, that is to say, a system for the conversion of one form of energy 

 to another. Thus the steam-engine converts the potential energy of over- 

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

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

 ere 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. 



Protoplasm, which is the seat of all these changes in both plants and 

 animals, is active only within fairly narrow limits of temperature, approxi- 

 mately 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 con- 

 veyed with the food, it follows that all the energy with which we have to 

 1 is the energy of molecules in watery solution, the playground of whose 

 tivities is a jelly-like mass of colloidal material, heterogeneous yet struc- 

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

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

 OSMOTIC PRESSURE. If we place two gas jars together, mouth to 

 mouth, as in Fig. 19, the upper jar containing hydrogen and the lower jar 

 me heavier gas, such as oxygen or carbon dioxide, within a very short time 



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