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"He saved more lives than Napoleon took in all his wars."

See pages 168-170.

HUMAN BIOLOGY

CHAPTER I

THE GENERAL STRUCTURE OF THE HUMAN BODY

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1. Regions of the body. In man and in most other mammals one can distinguish at least three regions; namely, the head, neck, and trunk. To the trunk are attached two pairs of appendages; namely, two arms and two legs, or, as they are more often called in the descriptions of the lower animals, the four legs. If the front wall of the trunk (composed largely of skin and muscle) were removed, it would be found that this region of the human body is divided into an upper story or chest cavity (Fig. 1), and a lower story or abdominal cavity. These two cavities are separated from each other by a flexible partition called the diaphragm, which is composed largely of muscle more or less in the form of a dome. The chest and abdominal cavities, separated by a diaphragm, are characteristic of all mammals.

2. Organs of the body. When we study the body more closely, especially its interior, we find, in various regions, parts that carry on special kinds of work (Fig. 2). Within the chest cavity is the heart, which forces blood through the

1 Each of the structures named in this paragraph should be demonstrated on a manikin or a chart before the textbook lesson is assigned. While studying the lesson, the pupil should find in Fig. 2 each of the organs named.

body. Here, also, are the lungs, which take in oxygen and give it to the blood, and which remove carbon dioxid, water, and other waste matters from the blood. Below the diaphragm are the stomach and the intestines, the liver and the

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FIG. 1.-Longitudinal section of trunk (side view).

pancreas, all of which help to change our food into liquia form ready to be used by the body. All these and other parts of the body are called organs. An organ is a part of a living body that has some special work to do; this special work is called its function. Our hands, for example, are organs

because with them we do some special work like writing, sewing, or playing the piano.

3. Tissues of the body.

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When we squeeze the arm or the hand, we feel the hard bones within that form the skele

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FIG. 2.- Organs of chest and abdomen (front view).

ton. We can raise from the bones the softer fleshy material, which is composed of muscle covered by skin. By clenching the fingers tightly we can see and feel on the inner side of the wrist the tough cords or tendons of connective tissue that

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