PHYSIOLOGICAL CHEMISTRY. 



CHAPTER I. 

 INTRODUCTION. 



IT follows from the law of the conservation of matter and of energy that 

 living beings, plants and animals, can produce neither new matter nor 

 new energy. They are only called upon to appropriate and assimilate 

 material already existing and to transform it into new forms of energy. 



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 proteins, carbohy- 

 drates, fats, resins, organic acids, etc. The chemical work which is per- 

 formed 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 radiant energy of the sunlight induces the green 

 parts of the plant to split off oxygen from the carbon dioxide and water 

 and this reduction is generally considered as the starting-point in the 

 syntheses that follow. According to a hypothesis suggested by A. 

 BAEYER, 1 formaldehyde is first produced, CO2 + H 2 O = CH 2 O + O2, which 

 by condensation is transformed into sugar. From the sugar other bodies 

 can then be built up. 



With the aid of the silent electric discharge W. LOEB 2 has succeeded 

 in obtaining from carbon dioxide and water, formaldehyde, and as a 

 product of polymerization, also glycolaldehyde, CH 2 OH.CHO, from 

 which sugar can be readily produced. Still the conditions under which 

 these bodies were formed cannot be applied to the conditions in the plants. 

 The investigations of USHER and PRIESTLEY 3 are of greater interest 



1 Ber. d. d. chem. Gesellsch., 3. 

 2 Zeitschr. f. Electrochem., 12. 

 3 Proc. Roy. Soc. London, 78, Series B. 



