PAET II. 



PHYSIOLOGICAL CHEMISTRY. 



ELEMENTAKY COURSE. 



INTRODUCTION. 



PHYSIOLOGICAL Chemistry or Chemical Physiology is the subject 

 which treats of the chemical processes connected with life. It com- 

 prises a study of the chemical constitution of the various tissues and 

 of the chemical nature of the constant interchanges undergone by the 

 food-stuffs in their passage through the organism. 



Plants, under the influence of the sun's rays, have the power of 

 combining the various simple substances absorbed by the roots and 

 leaves into complex organic compounds. Their chemical processes 

 are, therefore, of the nature of * syntheses.' The complex bodies thus 

 produced have, locked up in their molecules, a large amount of 

 potential or latent energy. Animals eat the products of plant life 

 in order to obtain this energy. This they accomplish in their tissues 

 where the complex molecules are resolved into simpler ones and the 

 potential energy becomes liberated as actual or kinetic energy, which 

 is then used for the processes of life. Their chemical interchanges are 

 therefore of the nature of 'analyses' 



All the food-stuff, however, is not thus decomposed by the animal, a 

 certain amount of it being used in order to build up the tissues them- 

 selves (e.g. muscle, glands, etc.), and a certain amount being laid aside 

 as storage material (e.g. fat) available to the organism as food, should 

 the amount of this latter supplied from without be insufficient for the 

 needs of life. 



It will be seen, therefore, that the study of physiological chemistry 

 includes the chemical composition of the various food-stuffs and of the 

 tissues, as well as the nature of the chemical interchanges which these 

 food-stuffs undergo in the tissues. 



