VII. 



PHYSIOLOGICAL CHEMISTRY. 



50. CHEMICAL CHANGES IN PLANTS AND ANIMALS. 



General remarks. Physiological chemistry is that part of 

 chemistry which has more especially for its object the various 

 chemical changes which take place in the living organism of 

 either plants or animals. It considers the chemical nature of 

 the different substances used as "food," follows up the changes 

 which this food undergoes during its absorption and assimila- 

 tion in the organism, and treats finally of the products which 

 are eliminated by it. The chemical changes taking place in 

 the organism are either normal (in health) or abnormal (in dis- 

 ease). The abnormal products formed under abnormal condi- 

 tions are generally termed "pathological" products. 



Difference between vegetable and animal life. As a general 

 rule, it may be stated that the chemical changes in a plant are 

 progressive or constructive, in an animal regressive or destructive. 

 That is to say, plants take up as food a small number of inor- 

 ganic substances of a comparatively simple composition, convert 

 them into organic substances of a more and more complicated 

 composition with the simultaneous liberation of oxygen, whilst 

 animals take up as food those organic vegetable substances of a 

 complex composition, assimilate them in their system, where 

 they are gradually used (burned up) and finally discharged as 

 waste products, which are identical (or nearly so) with those 

 substances serving as plant food. 



