Page:Food and cookery for the sick and convalescent.djvu/30

8 Results have shown that the oxidation of foods is the same in the body as outside the body.

"The amount of heat given off in the oxidation of a given quantity of any material is called its 'heat of combustion,’ and is taken as a measure of its latent or potential energy." The calorie is the unit measure of heat used to denote the energy-giving power of food, and is equivalent to the amount of heat necessary to raise one kilogram of water 1° C. or about one pound of water 4° F.

While proteids are capable of furnishing heat and energy as well as building and repairing tissues, it must always be remembered that their chief office is for the latter work. It is impossible for metabolism to go on without the production of some heat. The proteids are the only foods that contain nitrogen.

To determine the amount of nitrogen in a given food stuff, divide its grammes of proteid by 6.25. One gramme nitrogen equals 6.25 grammes proteid. The excretion of nitrogen for a man of average weight is about twenty grammes daily, the same amount being consumed. When the quantity of nitrogen is increased, there is a corresponding increase of its excretion, thus establishing nitrogenous equilibrium.