ALBUMINOIDS. FATS. CARBOHYDRATES. Oatmeal 12 6 60 Milk 4 3 5 Butter 2 88 — Let o = number of ounces of oatmeal required. m = „ „ milk „ b = „ „ butter „ Then (12o + 4m + 2b)∕100 = 4.5 ozs. of albuminoid (6o + 3m + 88b)∕100 = 3 ozs. of fat (60o + 5m)/100 = 14.25 ozs. of carbohydrate, according to Moleschott’s diet. When these equations are worked out by substitution and transference— o = 19.2 ounces. m = 55.4 „ b = 0.24 „ _Similarly if it is required to find how much meat, bread, and butter of the following percentage composition will be required to give a man a sufficient amount of albuminoids, fats, and carbohydrates._ ALBUMINOIDS. FATS. CARBOHYDRATES. Meat 25 15 0 Bread 8 1.5 50 Butter 2 88 0 Let m = number of ounces of meat required. b = „ „ bread „ B = „ „ butter „ Then 12m + 8b + 2B/100 = 4.5 ozs. of albuminoid (15m + 1.5b + 88B)/100 = 3 ozs. of fat 50b/100 = 14.25 ozs. of carbohydrates When these equations are worked out— m = 6.28 ounces. b = 28.5 „ B = 1.15 „ =Relation of Food to Mechanical Work.=—In the body the movements of every part are constant sources of heat. It is evident therefore that the potential energy of food can be expressed by (_a_) the amount of heat obtained by its complete combustion, or (_b_) by the amount of work capable of being obtained from it. Joule discovered by exact experiment that the mechanical power obtainable from a given amount of fuel is directly proportional to the amount of fuel used, being in fact due to the oxidation of this fuel, the heat produced being transformed into mechanical power. The _heat unit_ or calorie has been already given (p. 32). The gram-metre is the _work unit_. The heat unit corresponds to 425.5 units of work. Thus the same energy required to heat one gramme of water 1° C. will raise a weight of 425.5 grammes to the height of 1 metre. Conversely a weight of 425 grammes if allowed to fall from a height of 1 metre, will by its concussion produce heat sufficing to raise the temperature of 1 gramme of water 1° C. In England the amount of work done is commonly expressed as foot tons, _i.e._ tons lifted one foot; while in France it is similarly expressed as kilogrammetres. Gramme-metres can be converted into foot-pounds by multiplying them by .007233, and kilogrammetres into foot-tons by dividing by 311. Frankland estimated that—