THE SCIENCE OF HAPPINESS 



better able to apply intelligent discrimination between 

 seemingly conflicting practical experiences, if we bear 

 in mind the underlying character of that need which 

 expresses itself as a desire for food. To the same end, 

 it will be well to carry our physiological explanations 

 one step farther, noting the chemical character of the 

 materials which supply mankind with food. For this 

 purpose, we may for the moment overlook the ever- 

 present supply of gaseous food in the form of oxygen, 

 that is taken into the body through the lungs, and the 

 equally essential liquid food-stuff in the form of the 

 universal solvent, water. 



Paying heed rather to the solid and semi-solid sub- 

 stances that are more conventionally thought of as 

 food-stuffs, we find that these great as is their seeming 

 diversity are all susceptible of being sorted into three 

 classes, which the physiological chemist designates 

 (i) proteins, (2) carbohydrates, and (3) fats. 



Proteins, or albuminoid substances, are such as 

 contain nitrogen combined with oxygen, carbon, 

 hydrogen, and sundry other elements in lesser quan- 

 tities. The essential condition, from a chemical stand- 

 point, is the presence of the nitrogen. Proteins are 

 often spoken of as nitrogenous foods. Familiar ex- 

 amples of this class of food are furnished by meat of 

 all kinds; eggs and milk also contain albuminoids, 

 and so do such vegetables as the cereals, and, in par- 

 ticular, lentils, peas and beans. 



Carbohydrates are so called because they are com- 

 posed of carbon, hydrogen, and oxygen. The sugars 

 and the starches are the typical carbohydrate foods. 



[278] 



