CHAPTER III. 



CHEMICAL BASIS OF THE BODY. 



IT seems natural to commence the description of the molecular 

 changes that take place in the various tissues and organs of the 

 body, with a brief account of the chemical composition 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 familiarity 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 ) oxygen, (2) car- 

 bon, (3) hydrogen, (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, so- 

 dium, magnesium, calcium and iron, are indispensable to the econ- 

 omy, and are widely distributed, but are found in comparatively 

 minute quantities. Occasionally traces of zinc, lead, copper, lith- 

 ium, and other minerals may be detected, but these must be re- 

 garded rather as accidental than indispensable ingredients. 



