Laboratory demonstration by means of (a) human skeleton and (b) manikin to show the position and gross structure of the chief organs of man.
Man and his Environment.—In the last chapter we saw that one factor in the improvement of man lies in giving him better surroundings. It will be the purpose of the following chapters to show how man is fitted to live in the environment in which he is placed. He comes in contact with air, light, water, soil, food, and shelter which make his somewhat artificial environment; he must adapt himself to get the best he can out of this environment.
The Needs of Living Things.—We have already found that the primary needs of plants and animals are the same. They both need food, they both need to digest their food and to have it circulate in a fluid form to the cells where it will be used. They both need oxygen so as to release the energy locked up in their food. And they both need to reproduce so that their kind may be continued on the earth. What is true of plants and other animals is true of man.
The Needs of Simple and Complex Animals the Same.—The simplest animal, a single cell, has the same needs as the most complex. The cell paramœcium feeds, digests, oxidizes its food, and releases energy. The cells of the human body built up into tissues have the same needs and perform the same functions as the paramœcium. It is the cells of the body working together in groups as tissues and organs that make the complicated actions of man possible. Division of labor has arisen because of the complex needs and work of the organism.
The human body seen from the side in longitudinal section.
The Human Body a Machine.—In all animals, and the human animal is no exception, the body has been likened to a machine in that it turns over the latent or potential energy stored up in food into kinetic energy (mechanical work and heat), which is manifested when we perform work. One great difference exists between an engine and the human body. The engine uses fuel unlike the substance out of which it is made. The human body, on the other hand, uses for fuel the same substances out of which it is formed; it may, indeed, use part of its own substance for food. It must as well do more than purely mechanical work. The human organism must be so delicately adjusted to its surroundings that it will react in a ready manner to stimuli from without; it must be able to utilize its fuel (food) in the most economical manner; it must be fitted with machinery for transforming the energy received from food into various kinds of work; it must properly provide the machine with oxygen so that the fuel will be oxidized, and the products of oxidation must be carried away, as well as other waste materials which might harm the effectiveness of the machine. Most important of all, the human machine must be able to repair itself.
In order to understand better this complicated machine, the human body, let us briefly examine the structure of its parts and thus get a better idea of the interrelation of these parts and of their functions.
Skeleton of a man. CR., cranium; CL., clavicle; ST., sternum; H., humerus; V.C., vertebral column; R., radius; U., ulna; P., pelvic girdle; C., carpals; M., metacarpals; Ph., phalanges; F., femur; Fi., fibula; T., tibia; Tar., tarsals; MT., metatarsals.