None of these constituents of the body remain permanently in the system, and whilst the old particles are being removed new ones are supplied by the food. It is calculated that in this way a quantity of material, equal to the weight of the whole body, is carried away every forty days. So that we may be said to moult or cast away our old body and get a new one every forty days.
The materials for the food of man, and containing the above elements, are derived from the mineral, vegetable, and animal kingdoms. The vegetable kingdom, however, is the great source of food to man and animals, as it is in the cells of the plant that the elements undergo those chemical changes which fit them for food. The animal can only supply what it obtains from them, and the substances supplied by the animal kingdom as food are identical with those obtained from plants.
The Food Collection is arranged as nearly as possible in the order of the following Classification, commencing at the western end of the lower gallery.
Class I. Alimentary or Necessary.
Group 1. Mineral Substances.
Examples: Water; Common Salt; Ashes of Plants and Animals.
Group 2. Non-nitrogenous force-producing Substances, incapable of forming Flesh or Muscle.
Examples: Sago, Arrowroot (Amylaceous); Sugar, Figs, Dates (Saccharine); Animal and Vegetable Fats and Oils (Oleaginous).
Group 3. Nitrogenous Substances capable of producing both Flesh and Muscle.
Examples: Eggs (Albuminous); Wheat, Flesh (Fibrinous); Peas, Cheese (Caseinous).