FOOD 23S 



much more readily. Have you not seen how easily 

 the fat catches fire when steak is broiled ? Fats are im- 

 portant in our diet especially for their fuel value; they 

 help to keep us warm; we eat more of them in winter than 

 in summer. 



Proteins. The third great class of foods is the class 

 called proteins, and now we have reached a subject concern- 

 ing which our ignorance is greater than our knowledge. 

 For the science of chemistry has not yet revealed the exact 

 composition of the molecules of proteins; we cannot write 

 a chemical formula for them as we can for fats and carbo- 

 hydrates. Why not? Simply because these substances 

 are so complex that they defy chemical analysis. As 

 soon as the chemist begins to work with them, their mole- 

 cules "break down" into other substances. Then all he 

 can do is to determine what are the elements which com- 

 pose their molecules. As to the proportions of these ele- 

 ments in the protein molecule, or as to how they are ar- 

 ranged with reference to one another, he is quite at a loss 

 to tell. So you see why we have no definite formulas for 

 protein molecules; our knowledge of them is quite limited. 



Yet we do know that proteins contain all the elements 

 that carbohydrates and fats contain, and a number of 

 others besides. Of these others, nitrogen is the most 

 conspicuous. Indeed, it is so conspicuous that it is cus- 

 tomary to speak of the proteins as nitrogenous foods, and 

 of all others as non-nitrogenous foods. Other elements 

 present in proteins in minor and varying amounts are 

 phosphorus, iron, and sulphur. 



Proteins are essential for the growth and repair of the 

 body. They are the great tissue-formers. Our muscles 



