CHAPTER IY. 



THE CHEMICAL COMPOSITION OF THE BODY. 



OF the known chemical elements of which about seventy have been 

 isolated no less than seventeen combine, in larger or smaller quantities, 

 to form the chemical basis of the animal body. 



The substances which contribute the largest share are the non-metallic 

 elements, Oxygen, Carbon, Hydrogen, and Nitrogen oxygen and carbon 

 making up altogether about 85 per cent of the whole. The most abun- 

 dant of the metallic elements are Cv.lcium, Sodium, and Potassium.* 



Few of the elements, however, appear free or uncombined in the ani- 

 mal body. They are generally united together in variable proportions to 

 form compounds. The only elements which have been found free in the 

 body are oxygen, nitrogen, and hydrogen, the first two in the blood, and 

 hydrogen as well as oxygen and nitrogen in the intestinal canal. 



It was formerly thought that the more complex compounds built up 

 by the animal or vegetable organism were peculiar and could not be made 

 artificially by chemists, and under this idea they were formed into a dis- 

 tinct class, termed oryunu'. This idea has long been given up, but the 

 name is still in use with a different signification. The term is now ap- 

 plied simply to the compounds of the element carbon, irrespective of their 

 origin. 



A large number of the animal organic compounds, particularly those 

 of the albuminous group, are characterized by their complexity. Many 

 elements enter into their composition, thereby distinguishing them from 

 simple inorganic compounds. Many atoms of the same element occur in 

 each molecule. This latter fact no doubt explains the reason of their 

 instability. Another great cause of the instability is the frequent pres- 

 ence of nitrogen, which may be called negative or undecided in its affini- 

 ties and may be easily separated from combination with other elements. 



*The following table represents the relative proportion of the various ele- 

 ments. (Marshall.) 

 Oxygen . 72.0 



Carbon 13.5 



Hydrogen 9.1 



Nitrogen . . . , 2.5 

 Cfilci'um . . . . .13 



Phosphorus . . . . 1.15 



Sulphur ..... .1476 



Sodium .... .1 



Chlorine . . . ^085 



Fluorine 08 



Potassium ..... .026 



Iron 01 



Magnesium ..... .0012 



Silicon 0002 



(Traces of copper, lead, and alu- 



minum) 



no 



100. 



