CHAPTER I 

 CHEMICAL COMPOSITION OF THE HUMAN BODY 



THE fifteen elements of which the body is composed are 

 present in about the following proportions : 



Carbon, 18.5$ Oxygen, 65.0$ 



Hydrogen, \\.Q% Nitrogen, 2.5$ 



Sulphur, Phosphorus, Chlorine, Iodine, Fluorine, Silicon, 



Potassium, Sodium, Calcium, Magnesium, Iron, together 



3#- 



The adult human body contains about 3 g iron. Other ele- 

 ments, traces of which are sometimes found, must be regarded as 

 accidental constituents. 



The body is, therefore, mainly composed of non-metals 

 (metalloids). 



Oxygen, nitrogen, and, in small quantities, hydrogen are the 

 only free elements; only the free oxygen is of physiological im- 

 portance. 



The greater part of these and all other elements are found in 

 both inorganic and organic compounds, in which they take the 

 following parts, in detail : 



1. Carbon forms the basis of all the organic compounds of our 

 body. It unites with hydrogen and oxygen to form fats and 

 carbohydrates; with hydrogen, oxygen, nitrogen, and sulphur, to 

 form proteid bodies. It is, therefore, a constituent of the meta- 

 bolic products of these substances and this chiefly in the form of 

 carbonic acid, which is found throughout the body, partly in the 

 free state, partly in the carbonates or bicarbonates of the alkalies 

 and calcium. 



2. Hydrogen is mostly (f ) united with oxygen, forming, water. 

 With chlorine, it forms hydrochloric acid; with sulphur, sulphu- 

 retted hydrogen, found in the intestinal gases; with nitrogen, 

 ammonia and its salts. Above all, it is one of the chief constitu- 

 ents of the organic compounds. 



3. Nitrogen appears in the inorganic compounds only as 

 ammonia, being united with hydrogen. It is found, however, in 

 many organic compounds, of which the proteids with their deriva- 

 tives and metabolic products are the most important. 



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