MATTER AND ENERGY 85 



living matter. There is, however, another 

 way in which they may be taken up, when 

 they are not dissolved, but pass into the 

 colloidal matter in virtue of some affinity for 

 it. This process is called adsorption. The 

 electrical state of the colloid influences this 

 process. Adsorption plays an important part 

 in physiological processes. 



43. Finally we have water, the general 

 solvent, and the medium by which the mole- 

 cules of the other bodies are brought so close 

 together as to permit of those reciprocal 

 actions on which life depends. About two- 

 thirds of the weight of the body consists of 

 water. 



44. Chemical Phenomena of Plant Life. 

 We can now form some conception of the 

 relation of matter and energy in the living body, 

 and we shall be assisted if we consider the 

 chemical phenomena of plant life and contrast 

 these with what happens in an animal. A 

 plant requires ammoniacal salts, water and 

 carbonic acid. These it derives from the 

 soil and the air, and ammoniacal com- 

 pounds that are mainly the result of chemical 



