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PHYSIOLOGICAL CHEMISTRY. 



CHAPTER I. 

 INTRODUCTION. 



IT follows from the law of the conservation of force and matter 

 that living beings, plants and animals, can neither produce new 

 matter nor new force. They are only called upon to appropriate 

 and assimilate already existing material and to transform it into 

 new forms of force. 



Out of a few relatively simple combinations, especially carbon 

 dioxide and water, together with ammonium compounds or nitrates, 

 and a few mineral substances, which serve as its food, the plant 

 builds up the extremely complicated constituents of its organism, 

 albumins, carbohydrates, fats, resins, organic acids, etc. The 

 chemical work which is performed in the plant must therefore, in 

 the majority of cases, consist in syntheses; but besides these, 

 processes of reduction take place to a great extent. The vis viva 

 of the sunlight induces the green parts of the plant to split off oxy- 

 gen from the carbon dioxide and water, and therefore the chief 

 constituents of the plant contain less oxygen than the material serv- 

 ing as food. The vis viva of the sun, which produces this splitting, 

 is not lost ; it is only transformed into another form of force, into 

 the potential energy or chemical tension of the free oxygen on the 

 one side and the combinations less oxygenated produced by the 

 synthesis, on the other side. 



These conditions are not the same in animals. They are de- 

 pendent either directly, as the herbivora, or indirectly, as the car- 



