Chapter XII

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46 The oxygen pressure of the atmosphere is that portion of the total atmospheric pressure which is due to the weight of the oxygen. Since oxygen comprises about one fifth of the atmosphere, the pressure which it exerts is about one fifth of the total atmospheric pressure, or, at the sea level, about three pounds to the square inch (15 x 1/5 = 3). This is the oxygen pressure of the atmosphere. The low oxygen pressure in the tissues is due to its scarcity, and this scarcity is due to its entering into combination at the cells.

47 See footnote on oxygen pressure, page 109.

48 The impression prevails to some extent that carbon dioxide, on account of its weight, settles out of the atmosphere, collecting in old wells and at the floor in crowded rooms. Any such settling of the carbon dioxide is prevented by the rapid motion of its molecules. This motion not only prevents a separation of carbon dioxide and air after they are mixed, but causes them to mix rapidly when they are separated, if they still have surface contact. The carbon dioxide found in old wells is formed there by decaying vegetable or animal matter. In rooms it is no more abundant at the floor than in other parts.

49 On account of the formation of carbon dioxide in places containing decaying material, the descent into an old well or other opening into the earth is often a hazardous undertaking. Before making such a descent the air should always be tested by lowering a lighted lantern or candle. Artificial respiration is the only means of restoring one who has been overcome by this gas (page 97).

50 While awaiting oxidation at the cells, the carbohydrates and fats are stored up by the body, the carbohydrates as glycogen and the fats as some form of fat. In this sense they are sometimes looked upon as serving to build up certain of the tissues.

51 The following table shows the main elements in the body and their relation to the different nutrients:

[Nutrient Table]

52 The recently advanced theory that the molecules of the mineral salts, by dissolving in water, separate into smaller divisions, part of which are charged with positive electricity and part with negative electricity, has suggested several possible uses for sodium chloride and other mineral salts in the body. The sodium chloride in the tissues is in such concentration as to be practically all separated into its sodium and chlorine particles, or ions. It has recently been shown that the sodium ions are necessary for the contraction of the muscles, including the muscles of the heart. There is also reason for believing that the different ions may enter into temporary combination with food particles, and in this way assist in the processes of nutrition.

53 Chittenden, _The Nutrition of Man_.

54 Compiled from different sources, but mainly from Atwater's _Foods: Nutritive Value and Cost_, published by the U.S. Department of Agriculture.

55 The calorie is the adopted heat unit. As used in this table it may be defined as the quantity of heat required to raise 1 kilogram (2.2 pounds) of water, 1 degree centigrade. The calories also show the relative amount of energy supplied by the different foods.

56 While alcohol cannot be classed as a food, it is believed by some authorities to contain _food value_ and, in the hands of the physician, to be a substance capable of rendering an actual service in the treatment of certain diseases. It might, for example, be used where one's power of digestion is greatly impaired, since alcohol requires no digestion. But upon this point there is a decided difference of opinion. Certain it is that no one should attempt to use alcohol as food or medicine except under the advice and direction of his physician.

57 A layer of connective tissue between the mucous membrane and the muscular coat is usually referred to as the _submucous_ coat. This contains numerous blood vessels and nerves and binds the muscular coat to the mucous membrane.

58 The saliva may continue to act for a considerable time after the food enters the stomach. "Careful examination of the contents of the fundus (large end of the stomach) by Cannon and Day has shown that no inconsiderable amount of salivary digestion occurs in the stomach."--FISCHER, _The Physiology of Alimentation_.

59 Perhaps the simplest method of inducing vomiting is that of thrusting a finger down the throat. To make this method effective the finger should be held in the throat until the vomiting begins. An emetic, such as a glass of lukewarm salt water containing a teaspoonful of mustard, should also be taken, and, in the case of having swallowed poison, the vomiting should be repeated several times. It may even be advantageous to drink water and then vomit it up in order to wash out the stomach.

60 Hammerstein, _Text-book of Physiological Chemistry._

61 Amylopsin is absent from the pancreatic juice of infants, a condition which shows that milk and not starch is their natural food.

62 The fact that butter is more easily digested than other fatty substances is probably due to its consisting largely of a kind of fat which, on splitting, forms a fatty acid (butyric) which is soluble in water.

63 Fischer, _Physiology of Alimentation._

64 Beginning the meal with a little soup, as is frequently done, may be of slight advantage in stimulating the digestive glands. To serve this purpose, however, and not interfere with the meal proper, it should contain little greasy or starchy material and should be taken in small amount.

65 Dr. William Beaumont, an American surgeon of the last century, made a series of observations upon a human stomach (that of Alexis St. Martin) having an artificial opening, the result of a gunshot wound. Much of our knowledge of the digestion of different foods was obtained through these observations. In spite of the protests of his physician, St. Martin would occasionally indulge in strong drink and always with the same result--the lining of the stomach became much inflamed and very sensitive, and the natural processes of digestion were temporarily suspended.

66 The lacteals (from the Latin _lacteus_, milky) are so called on account of their appearance, which is white, or milk-like, due to the fat droplets.

67 Peptones and proteoses, when injected directly into the blood, are found to act as poisons.

68 The soluble double sugars (maltose, milk sugar, and cane sugar) are reduced to the simple sugars (dextrose and levulose). Furthermore the action on the proteids does not stop with the production of peptones and proteoses, but these in turn are still further reduced.

69 Energy, which is defined as _the ability to do work_, or _to cause motion_, exists in two general types, or forms, known as kinetic energy and as potential energy. _Kinetic_ energy is energy at work, or energy in the act of producing motion; while _potential_ energy is reserve, or stored, energy. All moving bodies have kinetic energy, and all stationary bodies which have within them the _capability_ of causing motion possess potential energy. A bent bow, a piece of stretched rubber, a suspended weight, the water above a mill dam, all have the capability of causing motion and all have potential energy. Examples of kinetic energy are found in the movements of machinery, in steam and electricity, in winds, and in currents of water. Kinetic is the active, and potential the inactive, form of energy.

70 As the atoms of hydrogen and oxygen that make up the molecules of water separate, they unite with atoms of their own kind--the hydrogen with hydrogen and the oxygen with oxygen atoms. Since these combinations are weaker than those of the water molecules, energy is required to bring about the change. But when hydrogen burns in the oxygen, the change is from a weaker to a stronger combination. The stored-up energy is then given up or becomes active.

71 In the evaporation of water, the energy of the sun is stored with reference to the force of gravity. In evaporating, water rises as a gas, or vapor, above the earth's surface, but on condensing into a liquid, it falls as rain. It then finds its way through streams back to the ocean. All water above the sea level is in such a position that gravity can act on it to cause motion, and it possesses, on this account, potential or stored-up energy. It is because of this energy that rapids and waterfalls are such important sources of power.

72 Energy, like matter, can neither be created nor destroyed. It can, however, be transferred from one body to another and transformed from one form to another form. Whenever work is done, energy is transferred from the body doing the work, to the body upon which the work is done. During this process there may, or may not, be a transformation of energy. In turning a grindstone, kinetic energy is passed to the stone and used without transformation, but in winding a clock, the kinetic energy from the hand is transformed into potential energy in the clock spring. Then as the clock runs down this is retransformed into kinetic energy, causing the movements of the wheels.

Not only is kinetic transformed into potential energy and _vice versa_, but the different forms of kinetic energy (heat, light, electricity, sound, and mechanical motion) are readily transformed the one into the other. With suitable devices, mechanical motion can be changed into heat, sound, or electricity; heat into motion and light; and electricity into all the other forms of energy. These transformations are readily explained by the fact that the different varieties of kinetic energy are but different forms of motion (Fig. 84).

73 The simplest arrangement of the parts of a gland is that where they are spread over a plain surface. This arrangement is found in serous membranes, such as the pleura and peritoneum. These membranes, however, are not called glands, but secreting surfaces.

74 In the oxidations that occur in the body it is not supposed that the nutrients are immediately converted to carbon dioxide, water, and urea. On the other hand, it is held that their reduction takes place gradually, as the reduction of sugar by fermentation, and that the wastes leaving the body are but the "end products" and show only the final results.

75 Alcohol, if used in considerable quantity, leads to cirrhosis of the liver and Bright's disease of the kidneys, both very dangerous diseases. Dr. William Osler in his treatise, _The Practice of Medicine_, states that alcohol is the chief cause of cirrhosis of the liver. Dr. T.N. Bogart, specialist in kidney diseases, asserts that one third of all the cases of Bright's disease coming under his observation are caused by alcohol.

76 Hall, _The Purin Bodies_.

77 Review "Main Physiological Problems," page 21.

78 In the production of motion in the body, as well as in the production of any kind of _purposeful_ motion outside of the body, three conditions must be fulfilled. There is required, in the first place, a mechanical device or machine which is so constructed as to produce a certain kind of motion. In the second place, energy is needed to operate this device. And, finally, there must be some controlling force, by means of which the motion is made to accomplish definite results. The driving of a horse hitched to a wagon will illustrate these conditions. The wagon is the mechanical device, the horse furnishes the energy, and the driver supplies the controlling force. In this, as in most cases, the machinery, the source of energy, and the controlling force are disconnected except when at work; but in the body all three occur together in the same structure.

79 The dependence of the outer layers of bone cells upon the periosteum for nourishment causes a destruction of this membrane to affect seriously the bone beneath, producing in many instances a decay of the bone substance.

80 It has been claimed that the introduction of vertical writing has reduced the number of cases of spinal curvature originating in the schoolroom, and statistics appear to prove the claim. It is shown, on the other hand, that unnatural positions also are unnecessary in the slanting system of writing, and that in either system the pupil who is permitted to do so is liable to assume an improper position.

81 Lovett, _Lateral Curvature of the Spine and Round Shoulders_.

82 See "Hygiene of Muscles,"