[Illustration:  FIG. 26.—­The bomb calorimeter from which the fuel value of food can be estimated.]

The fuel value of a food is determined by means of the bomb calorimeter (Fig. 26).  The food substance is put into a chamber A and ignited, and the heat of the burning substance raises the temperature of the water in the surrounding vessel.  If 1000 grams of water are in the vessel, and the temperature of the water is raised 2 deg.  C., the number of calories produced by the substance would be 2000, and the fuel value would be 2000 calories.[A] From this the fuel value of one quart or one pound of the substance can be determined, and the food substance will be said to furnish the body with that number of heat units, providing all of the pound of food were properly digested.

[Footnote A:  As applied to food, the calorie is greater than that used in the ordinary laboratory work, being the amount of heat necessary to raise the temperature of 1000 grams of water 1 deg.  C., rather than 1 gram 1 deg.  C.]

    TABLE SHOWING THE NUMBER OF CALORIES FURNISHED BY
    ONE POUND OF VARIOUS FOODS
  ----------------------------------------------------
  |FOOD |CALORIES|FOOD |CALORIES|
  ----------------------------------------------------
  |Leg of lean mutton | 790|Carrots | 210|
  ----------------------------------------------------
  |Rib of beef | 1150|Lettuce | 90|
  ----------------------------------------------------
  |Shad | 380|Onion | 225|
  ----------------------------------------------------
  |Chicken | 505|Cucumber | 80|
  ----------------------------------------------------
  |Apples | 290|Almonds | 3030|
  ----------------------------------------------------
  |Bananas | 460|Walnuts | 3306|
  ----------------------------------------------------
  |Prunes | 370|Peanuts | 2560|
  ----------------------------------------------------
  |Watermelons | 140|Oatmeal | 4673|
  ----------------------------------------------------
  |Lima beans | 570|Rolled wheat | 4175|
  ----------------------------------------------------
  |Beets | 215|Macaroni | 1665|
  ------------------------------------------------
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57.  Varied Diet.  The human body is a much more varied and complex machine than any ever devised by man; personal peculiarities, as well as fuel values, influence very largely the diet of an individual.  Strawberries are excluded from some diets because of a rash which is produced on the skin, pork is excluded from other diets for a like reason; cauliflower is absolutely indigestible to some and is readily digested by others.  From practically every diet some foods must be excluded, no matter what the fuel value of the substance may be.