172 ANATOMY FOR NURSES. [CHAP. XIV. 



Of these substances, chloride of soda, sodium chloride or com- 

 mon salt, is the most important mineral ingredient of food. It 

 is contained in nearly everything we eat, but usually not in 

 sufficient quantity to supply all the needs of the body, and we 

 therefore add it as a separate article of diet. It is present in 

 most of the fluids of the body, notably in the blood. The rest 

 of the mineral substances are usually contained in sufficient 

 quantity in an ordinary diet, though occasionally it becomes 

 necessary to supply them independently. Of all the mineral 

 salts, phosphate of lime exists in the largest quantity in the 

 body ; it enters largely into the composition of the bones, teeth, 

 and cartilages, and gives firmness and solidity to the tissues. 

 It is present in very small quantities in the bodily fluids, with 

 the exception of the milk, which contains a notable amount of 

 phosphate of lime, and which serves for the ossification of the 

 growing bones of infants and young children. 



Chemical composition of the body. Professor Atwater gives 

 the following average composition of the body of man, weigh- 

 ing 148 pounds : 



Oxygen 92.4 



Carbon . . , 31.3 



Hydrogen 14.6 



Nitrogen 4.6 



Calcium 2.8 



Phosphorus 1.4 



Potassium 34 



Sulphur 24 



Chlorine 12 



Sodium .12 



Magnesium .04 



Iron 02 



Fluorine 02. 



The human body, from a chemical point of view, may be 

 regarded as a mixture of three large classes of chemical sub- 

 stances ; viz. proteids, fats, and carbo-hydrates associated with 

 water and mineral salts. 



In our first chapter we said that protoplasm was the basis of 

 the life of the body, and from that point of view we may look 

 upon the human body as an assemblage of variously modified 

 protoplasm. But it comes to the same thing, for the chemical 



142.9 



5.1 



