CHAPTER XLV. SKELETAL SYSTEM.. General; Regions of the skeleton; The head; The trunk; Ribs and sternum; Bones of limbs; Composition of bone; Growth of bone; Joints; Hygiene of the skeleton. CHAPTER XLVI. MUSCULAR SYSTEM.. Importance; Structure; Blood and nerve supply; Action of muscles; Results of muscular action; Exercise. CHAPTER XLVII. NERVOUS SYSTEM... Introduction; Parts of nervous system; The nerve cell; Nerves; The brain; Functions of brain; Spinal cord; Sym- pathetic nervous system; Action of nervous system; Reflex actions; Voluntary action; Habits; Education; Care of CHAPTER XLVIII. THE SPECIAL SENSES.. General; Touch; Temperature; Taste; Smell; Eye; Struc- ture; Light; Lenses; Images; Focusing; Defects of the Importance of health; Health and disease; Cause of dis- ease; How germs enter the body; Growth of germs; How A YEAR IN SCIENCE CHAPTER I MATTER What we understand by Science. The subject with which we are about to deal in this study is Science. To many this is a new study, and, no doubt, ideas of its meaning differ widely. However, we shall learn, as we proceed with this work, that we are dealing with very common things and common changes that are going on about us daily. Some of the subjects we shall study, perhaps we feel we know from our daily observations. All of us know that water flows down hill and not up; that a stone thrown into the air returns to the earth again. Have we stopped to learn why? To answer these and similar questions is the work of science. It deals with seeking truths concerning nature. The field of science is usually sub-divided into the natural sciences and the physical sciences. The natural sciences deal with living material, plants and animals. To the study of plants the name Botany is given, to the study of animals, Zoology. The physical sciences deal with inanimate material in all its forms and with the changes and processes to which it is subject. Some of the physical sciences are Chemistry, Physics, and Physical Geography. Chemistry deals with changes in substances which result in the formation of new substances. For instance, the burning of wood is a chemical process. Physics treats of changes and processes that do not result in the formation of other substances. In Physical Geography a study is made of weather, climate, and land forms, and their relation to man. Definition of matter. For the substance dealt with Fig. 1. If an inverted tumbler is pushed mouth downward into water, the air within the tumbler keeps the water from entering it. in this general science the term matter is used. According to most authors, matter is anything which occupies space or has weight. Thus it will be seen at once that wood is matter, and that water is matter. Matter, however, does not exist in visible form only, for gases, too, are matter. Is air matter? An empty tumbler, that is, a tumbler which does not contain anything that can be seen, is pushed mouth downward half under the surface of the water in a glass jar. The water rises in the tumbler only about of an inch. Evidently there is something within the tumbler which prevents the water from rising to fill it. The tumbler is then tilted sidewise until the mouth comes just above the surface of the water. Bubbles of air escape. If the tumbler is then again pushed into the water, the water will rise into it. Evidently, in the first instance, it was air that kept the water from rising into the tumbler. Since the water rose higher in the tumbler Fig. 2. A globe was balanced after part of the air was pumped from it. It was found to be heavier after the air was again allowed. to enter it. after the air had escaped, this experiment proves that air occupies space. In fact, air is present usually in spaces which appear empty. A hollow brass globe fitted with a stop cock is accu rately weighed. With an air pump the air is exhausted from the globe and the stop cock is closed. The globe is again weighed. It is found to weigh more when filled with air than it does after the air has been exhausted. Air therefore has weight. Since air occupies space and also has weight, according to the definition of matter, air is matter. Air is a gas, so we have proved that a gas is matter. Three forms of matter. All material exists in one of three forms: solid, liquid, and gas. If a substance has definite size and shape, we call it a solid. The shape of a solid can not be changed except by some external force. If the size of a substance is definite, but the shape depends upon the containing vessel, it is a liquid. Gases have neither definite size nor shape, and they expand without limit. The behavior of these three forms of matter, and the changes which they undergo under different conditions, will be studied in the following chapters. Questions 1. With what does the subject of science deal? 2. Into what two divisions is science naturally divided? 3. What is meant by the words animate and inanimate? 4. Name the two natural sciences. How do they differ from each other? 5. Name three physical sciences. Of what does each treat? |