FIG.

71. A DEVICE FOR THE REMOVAL OF THE RESPIRATORY PRODUCTS FROM THE RESPIRATION CHAMBERS.

much of the protein leaves the body as comparatively complex substances, urea and the like, which in the calorimeter undergo oxidation.

Food requirements.-By the use of various forms of calorimeters, by the examination of excreta by various experiments, and by investigations of the amount of food eaten by healthy individuals in different countries and engaged in various occupations, it has been found that the amount of food that an individual requires is dependent chiefly upon the rate at which oxidation occurs in the body, and variations in this are largely due to differences in the muscular contraction that occurs. This, in turn, is dependent upon such things as the mode of life, age, sex, climate: for certain occupations and exercises entail more muscular contraction than others; cold increases muscular contraction, as is shown by the phenomenon of shivering, and it tends to induce an individual to exercise and make active movements, while warmth has the opposite effect; a strong person will expend more energy in his movements than a weak person, and a large person has a greater area of muscular surface to undergo contraction than a small person.

As oxidation uses up the fuel and muscular contraction increases the rate of oxidation, the greater the amount of muscular contraction an individual's conditions and manner of living entail, the more food will he require. It has been found, by the means mentioned in the preceding paragraph, that a man of average weight (about 59.5 kilograms—155 pounds) requires under differing conditions the following amounts of food:

When at rest, enough to yield 2000 calories.