Public School Domestic Science. Adelaide Hoodless

target="_blank" rel="nofollow" href="#ulink_64b9e620-d4bb-5099-9793-12c67a00d35c">[3] An illustration of vapor rising may be given by breathing upon a mirror.

CHAPTER II.

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Food Classification.

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      The following are familiar examples of compounds of each of the four principal classes of nutrients:

      Protein:

       Proteids.

      Albuminoids, e.g., albumen of eggs; myosin, the basis of muscle (lean meat); the albuminoids which make up the gluten of wheat, etc.

      Gelatinoids, constituents of connective tissue which yield gelatin and allied substances, e.g., collagen of tendon; ossein of bone.

      "Nitrogenous extractives" of flesh, i.e., of meats and fish. These include kreatin and allied compounds, and are the chief ingredients of beef tea and most meat extracts. Amids: this term is frequently applied to the nitrogenous non-albuminoid compounds of vegetable foods and feeding stuffs, among which are amido acids, such as aspartic acid and asparagin. Some of them are more or less allied in chemical constitution to the nitrogenous extractives of flesh.

       Fats.

      Fat of meat: fat of milk; oil of corn, wheat, etc. The ingredients of the "ether extract" of animal and vegetable foods and feeding stuffs, which it is customary to group together roughly as fats, include, with the true fats, various other substances, as lecithians, and chlorophylls.

      Carbohydrates, sugars, starches, celluloses, gums, woody fibre, etc.

      Mineral matter.

      Potassium, sodium, calcium and magnesium chlorids, sulphates and phosphates. (Atwater).

      The terms (a) "nitrogenous" and (b) "carbonaceous" are frequently used to designate the two distinct classes of food, viz.: (a) the tissue builders and flesh formers; (b) fuel and force producers.

      Each of these classes contains food material derived from both the animal and vegetable kingdom, although the majority of the animal substances belong to the nitrogenous, and the majority of the vegetable substances to the carbonaceous group.

      Therefore, for practical purposes, we will confine ourselves to the more general terms used in Atwater's table.

Uses of Food.

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      First, food is used to form the materials of the body and repair its waste; second, to yield energy in the form of (1) heat to keep the body warm, (2) to provide muscular and other power for the work it has to do. In forming the tissues and fluids of the body the food serves for building and repair. In yielding energy, it serves as fuel for heat and power. The principal tissue formers are the albuminoids; these form the frame-work of the body. They build and repair the nitrogenous materials, as those of muscle, tendon and bone, and supply the albuminoids of blood, milk and other fluids. The chief fuel ingredients of food are the carbohydrates and fats. These are either consumed in the body or are stored as fat to be used as occasion demands.

Water.

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      By referring to a preceding chapter we find that water composes three-fifths of the entire body. The elasticity of muscles, cartilage, tendons, and even of bones is due in great part to the water which these tissues contain. The amount of water required by a healthy man in twenty-four hours (children in proportion) is on the average between 50 and 60 ounces, beside about 25 ounces taken as an ingredient of solid food, thus making a total of from 75 to 85 ounces. One of the most universal dietetic failings is neglect to take enough water into the system. Dr. Gilman Thompson gives the following uses of water in the body:—

      (1) It enters into the chemical composition of the tissues; (2) it forms the chief ingredient of all the fluids of the body and maintains their proper degree of dilution; (3) by moistening various surfaces of the body, such as the mucous and serous membranes, it prevents friction and the uncomfortable symptoms which might result from drying; (4) it furnishes in the blood and lymph a fluid medium by which food may be taken to remote parts of the body and the waste matter removed, thus promoting rapid tissue changes; (5) it serves as a distributer of body heat; (6) it regulates the body temperature by the physical processes of absorption and evaporation.

Salts (Mineral Matter).—Use of Salts in Food.

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      (1) To regulate the specific gravity of the blood and other fluids of the body; (2) to preserve the tissues from disorganization and putrefaction; (3) to enter into the composition of the teeth and bones. These are only a few of the uses of salts in the body, but are sufficient for our purpose. Fruits and nuts contain the least quantity of salts, meat ranks next, then vegetables and pulses, cereals contain most of all (Chambers). Sodium chloride (common salt) is the most important and valuable salt. It must not however be used in excess. Potassium salts rank next in importance.[4] Calcium, phosphorus, sulphur and iron are included in this class.

      The quantity of salts or mineral matter contained in some important articles of vegetable and animal food is shown in this table (Church):