CHAPTER III. 



CHEMICAL BASIS OF THE BODY. 



It seems natural to commence the description of the molec- 

 ular changes that take place in the various tissues and organs 

 of the body with a brief account of the chemical compo- 

 sition of the most characteristic substances found in animal 

 textures, because none of the mysterious processes of cell life, 

 or tissue activity, can be satisfactorily studied without famil- 

 iarity with the more common terms occurring in physiological 

 chemistry. 



The chapter on this subject here introduced is intended rather 

 to give the medical student a general view of the chemical com- 

 position and characters of those substances most frequently met 

 with in the chemical changes specially connected with animal life, 

 than to supply a complete or systematic account of the relation- 

 ships of the chemical bases of the body, for which reference must 

 be made to more advanced text books, or treatises on the special 

 subject of physiological chemistry. This review must, moreover, 

 be inadequate in the case of many bodies, but they will be again 

 referred to when speaking of the function with which they are 

 associated. 



It has already been stated that of the sixty-three elements 

 known to chemists, a comparatively small number form the great 

 bulk of the animal body, although traces of many are constantly 

 present. Thus we shall see that four elements, namely, (1) oxy- 

 gen, (2) carbon, (3) hvdrogen, (4) nitrogen, are present in large 

 proportions in every tissue, and together make up about 97 per 

 cent, of the body ; and sulphur, phosphorus, chlorine, fluorine, 

 silicon, potassium, sodium, magnesium, calcium and iron, are 

 indispensable to the economy, and are widely distributed, but are 

 found in comparatively minute quantities. Copper is said to take 

 the place of iron in the blood of certain animals, octopus, etc. 

 Trequently traces of zinc, lead, lithium, and other minerals may 



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