Physiology and Hygiene for Secondary Schools

by Francis M. Walters

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.

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.

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).

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.

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.

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.

Hall, The Purin Bodies.

Review "Main Physiological Problems," page 21.

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.