CHAPTER IV 

 THE CHEMICAL COMPOSITION OF THE BODY 



A CONSIDERABLE number of the elements have been detected on 

 analysis of the dead bodies of the various forms of life found on the earth, 

 but the number composing the bodily structure of the higher animals 

 is strikingly few. The chief of these are carbon (C), hydrogen (H), 

 nitrogen (N), oxygen (0), phosphorus (P), sulphur (S), chlorine (Cl) 

 sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), and 

 iron (Fe). Others, such as iodine, boron, and fluorine, are found in 

 minute traces. The elements contained in the above list occur chiefly 

 in combination; some, however, such as nitrogen and oxygen, are 

 dissolved in the body fluids. , 



The chief chemical compounds which are obtained on dissociation 

 of the body may be grouped as (1) water, (2) inorganic compounds, 

 (3) organic compounds. 



Water is a constituent part of all tissues of the animal body, 

 the water content varying according to the nature and function 

 of the tissue from 50 to 90 per cent. The chief exceptions are 

 the enamel and cement of the teeth, which contain 0-2 per cent, 

 and 10 per cent, respectively. Adipose tissue contains 29 to 

 30 per cent, water, the brain 90 per cent., skin 72 per cent., muscles 

 76 per cent., lungs 79 per cent., heart 79-5 per cent., and the 

 lens of the eye 98-7 per cent, . The percentage in the body fluids 

 ranges from 79 per cent, in blood to 99-5 per cent, in sweat and 

 saliva. 



Inorganic Compounds. These are chlorides, phosphates, carbon- 

 ates, and sulphates. The chlorides are found chiefly as sodium 

 chloride. This salt may be extracted from all tissues and fluids. 

 More rarely found are the chlorides of potassium and 

 ammonium. 



The phosphates are also widely distributed, calcium and mag- 

 nesium phosphate occurring particularly in bone, of which the ash 

 contains respectively 85 to 90 of the former and 1-5 to. 1-9 per cent, 

 of the latter sal:. Soluble phosphates are also found in nearly all 

 the tissues and body fluids. 



The soluble carbonates and bicarbonates of the alkalies, sodium 

 and potassium, occur chiefly in the body fluids, helping to confer 

 upon these a slightly alkaline reaction to litmus. Insoluble car- 

 bonates occur in bone. 



