Chap. XV] CLASSIFICATION OF FOOD 287 



Salts. — The principal inorganic salts are : — 



Chloride 



Phosphate » ,. , , . 



^ , , > or sodium and potassium, 



bulphate 



Carbonate 



Phosphate 1 p , • , 



_, , > or calcium and magnesium. 



Carbonate J 



The inorganic salts are not oxidized in the body and therefore 

 do not yield energy, but they are an essential part of all the tissues, 

 and take part in the functions of the body in six ways: (1) they 

 maintain the alkaline or neutral reaction of the fluids of the body ; 

 (2) they furnish the material for the acidity or alkalinity of the 

 digestive fluids and other secretions ; (3) they help in regulating 

 the flow of fluids to and from the tissues, because they maintain 

 the normal osmotic pressure ; (4) they enter largely into the 

 composition of the bones, teeth, and cartilage ; (5) they are 

 necessary for the clotting of blood ; and (6) they give the fluids 

 of the body their influence upon the elasticity and irritability of 

 nerve and muscle. 



Proteins. — Proteins are complex compounds and consist of 

 carbon, hydrogen, nitrogen, oxygen ; sulphur, phosphorus, and 

 other elements may be present. They differ from carbohydrates 

 and fats in having nitrogen and therefore are described as nitroge- 

 nous compounds. They, occur in the form of : — 



Albumins. — Simple proteins that are soluble in water and 

 coagulable by heat. The white of egg when cooked, the scum 

 that forms on milk when it is heated, and the coating that forms 

 on meat when it has been subjected to high temperature are all 

 forms of albumin that have been coagulated by heat. 



Caseinogen. — If milk is allowed to stand until it sours, or if 

 the process is hastened by the addition of acid or rennet, the 

 caseinogen is formed into a curd. 



Gluten. — This is the starchy nitrogenous substance found in 

 wheat flour. 



Legumin. — This is a protein substance found in vegetables 

 that are classed as legumes, i.e. peas, beans, lentils, etc. 



Extractives. — These are protein substances found in plant 

 and animal bodies as a result of their metabolism. 



