Moisture. Every one of the' foods under discussion, no matter how 

 dry it may appear, contains some water which can be driven out by heat. 

 A high water content is not desirable, because it not only diminishes the 

 percentage of actual food material, but it also tends to cause the food to 

 mould or turn sour. Water has certain physiological functions to per- 

 form in the body, but it may be supplied from so many sources that it has 

 no particular value as a food. 



Protein is the name commonly given to a class of substances which 

 furnish the materials for the formation of bone, flesh, blood, etc. This 

 constituent is absolutely essential in the food of animals ; for, without it, 

 no animal can grow or even subsist. Moreover, the animal is totally 

 unable to create protein ; that is a function of plant life. The animal can 

 simply appropriate and transform the protein of plants into the particular 

 proteids of the body. Protein, when oxidized or burned in the body, will 

 produce heat, and if eaten in excess of that required for other purposes, 

 may form fat. Altogether protein is one of the most important constitu- 

 ents of a food, and the one which is the most expensive. Hence we natur- 

 ally like to find a food rich in this substance. 



Fat, or ether extract, is that part of the food which may be extracted 

 from the water-free material by ether, benzine, gasoline, etc. It is of 

 value for the formation of fat in the body and for the production of energy 

 and heat. For this latter purpose it has more than twice the value of 

 protein and carbohydrates. Fat may, therefore, be looked upon as a 

 concentrated heat producer. 



The Soluble Carbohydrates, or nitrogen-free extract, consist mainly 

 of starches, sugars, and closely allied compounds. In the cereal break- 

 fast foods these soluble carbohydrates form about two-thirds of the whole 

 material. Their particular function in the body is to form fat, or, when 

 oxidized, to produce heat and energy. They are frequently called the 

 energy or heat producers. 



Crude Fibre is the term applied to a group of substances which form 

 the woody or straw-like frame-work of plants. It is so indigestible that 

 it has almost no food value, and, further, it frequently renders the rest 

 of the food less digestible by protecting it from the action of the digestive 

 fluids. Therefore, a large amount of it in a food is not desired. Yet, it is 

 undoubtedly physiologically useful in giving the needed bulk to the food. 

 Ash is the inorganic or mineral part of foods. It is of great import- 

 ance in the food of the young, as it furnishes the phosphates, chlorides, 

 and other salts of calcium, magnesium, sodium, potassium, iron, etc., 

 which are needed in building up bone and the tissues of the body. 



Heat of Combustion. The various nutrients above referred to when 

 supplied in the food enable the body to o-row and to repair its tissues as 

 they are worn out in the necessary exercise of the body functions. They 

 also supply the body with the energy needed for doing work both internal 

 and external, and furnish the heat to keep the body warm. All the nutri- 

 ents, except the ash, may be oxidized or burned in the body, and are, 



