VII. 

 PHYSIOLOGICAL CHEMISTRY 



52. 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 assimilation in the organism, 

 and treats, finally, of the products eliminated by it. The chemical 

 changes taking place in the organism are either normal (in health) or 

 abnormal (in disease). The abnormal products formed under ab- 

 normal conditions 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 pro- 

 gressive or constructive, in an animal regressive or destructive. That is 

 to say, plants take up as food a small number of inorganic 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 

 these organic vegetable substances of a complex composition, assim- 

 ilating 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. 



Plant food. Waste products of animal life. 



Carbon dioxide. Carbon dioxide. 



Water. Water. 



Ammonia, NH 3 . Urea, CO(NH 2 ) 2 . 



Nitrates, MxNO 3 . Urates, MzC 5 H 2 N 4 O 3 - 



f Calcium. f Calcium. 



Phosphates > , M um Phosphates , , M ium . 



Sulphates - of Sulphates - of > 



[ Potassium. Chlorides Potassium. 



(420) 



