both develop heat and power to do work; and both give off certain waste matters. The horse, we may say, requires food, but so does the engine; for coal and water are as necessary for the development of heat and power in the engine, as food and water are for a similar purpose in the horse.

When we try to state characteristics that will distinguish all plants from all lifeless objects, we find the task still more difficult; for most plants do not move about from place to place, it is difficult to realize that they give off heat, and they do not give evidence that they have conscious feelings as do the common animals. In spite, however, of these similarities, we are usually able to distinguish living from lifeless objects at least by the three following characteristics.

2. Growth of Living Things. In the first place living things use some of the food they eat for growth. No one ever heard of an engine or other lifeless object beginning as a small machine, and then slowly growing larger until it comes to have many times its former weight. pens to all plants and all animals. instance, at birth weighs seven to eight weight is over twenty times as great. pare the weight of an oak tree with that of an acorn from which it started, the amount of increase we find to be enor

mous.

Yet this is what hapThe average child, for pounds; while a man's And if we try to com

3. Repair of Living Things. — In the second place, parts of a locomotive or of any other lifeless machine by continual use become worn or broken, and the engine must be sent to the machine-shop for repairs. Our bodies, too, are being constantly worn away; for every time we make a motion of

While it is true that icicles and other crystals apparently grow, this kind of growth is brought about wholly by the addition of mate rial to the outer surface.

any sort, some of our living muscle is used up; every time we think or exert our will power, some of the living brain substance is probably changed into dead waste material. But in contrast to lifeless machines, our bodies are self-repairing. The food we eat not only goes to increase the size of the body; it also furnishes material to make good the wear and tear of everyday life. This power of self-repair is likewise present in all animals and in plants as well.

4. Reproduction of Living Things. A third characteristic that distinguishes living things from those that are lifeless is the fact that they produce seeds (in the case of plants) or eggs (in the case of animals), which in turn come to form plants or animals like those by which these seeds or eggs were produced. No lifeless object can do this. We shall find in our laboratory study that, while there are a great many different methods of producing these new organisms, still in their essential features these various methods of reproduction are much the same from the lowest plants to the highest animals.

5. Summary. In brief, then, we may say that all living things have the power of growth from within, of self-repair, and of the reproduction of their kind; but that so far as we know lifeless objects possess none of these powers.

6. Science and its Subdivisions. Ever since the dawn of history we find that mankind has been seeking to learn the secrets of living and lifeless matter. During the past century our knowledge has increased so rapidly that many sciences have been completely rewritten. The discoveries, for example, of the characteristics of radium and of X-rays have revolutionized much of what was formerly believed as to the properties of lifeless matter. In the same way our increased knowledge regarding germs and other microscopic plants and

animals has made possible the scientific treatment of disease, and what is more important, the prevention of disease. As our knowledge of the living and lifeless world has increased, it has become necessary to divide this knowledge into a great many different branches, some of which are physics, chemistry, geology (a study of the earth), mathematics, psychology (a study of mind), and biology.

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7. Biology (from Greek, bi'os = life + lo'gos discourse) is the general name given to the study of all living things. Hence, this science treats of both animals and plants. If we confine our study to the structure and activities of plants alone, we call this part of the science plant biology, or botany. Animal biology, or zoology, on the other hand, treats of animals. So-called human physiology (better known as human biology) discusses man, the highest type of the animal kingdom; hence, it is a branch of the science of zoology, which in turn is one of the subdivisions of the study of biology.

CHAPTER II

COMPOSITION OF LIFELESS AND LIVING THINGS

8. Introduction. For a great many years scientists have been studying plants and animals, and from this study they have learned that the bodies of all living organisms, including human beings, are made from substances found in the water, soil, and air, and that when plants and animals cease to live, their bodies are changed into the chemical substances of which soil, air, and water are composed. We are now to learn by experiments the characteristics of some of these materials found in lifeless things, and some of the combinations of these materials in plants and animals.

I. ELEMENTS, COMPOUNDS, AND OXIDATION

Materials: Splinters of wood and pieces of carbon; starch, sugar, egg, meat; potassium chlorate, oxid of manganese, pieces of marble, zinc, hydrochloric acid, lime water (see below); elements for demonstration (e.g. phosphorus, sulphur, iron, magnesium); compounds for demonstration (e.g. magnesium sulphate, sodium nitrate, potassium nitrate, calcium phosphate, calcium carbonate); test tubes, thistle tube, apparatus stand, tray for collecting gases, delivery tube, cylindrical graduate or glass jar. (All of the materials named above will be found in the chemical or physical laboratory of almost every high school.)

Preparation of lime water: Put into a large bottle a good handful of lime (freshly slaked in water, if possible; air-slaked lime may be used, however). Fill the bottle with water, shake the mixture, and

allow it to stand until needed. Then pour some of the liquid through

a funnel in which is a filter paper. Collect the filtered lime water in a bottle, and keep it stoppered. As soon as it becomes cloudy, throw it away and obtain some more clear liquid by filtration as directed above. The large bottle can be kept indefinitely as a stock solution if it is kept filled with water.

9. Carbon (symbol, C). Laboratory Study No. 1. Suggested as home work.

1. Prepare some charcoal by lighting a long splinter of wood or a match and then blowing out the flame. (Pre

pared charcoal may be used.) Charcoal is nearly pure carbon.

a. Tell what you have done.

b. Is carbon (charcoal) a solid, a liquid, or a gas? What is its color?

c. Of what substance does this experiment prove that wood is partly composed?

2. Hold the tip of the carbon (charcoal) in a hot flame.

a. State what was done.

b. Does any of the carbon disappear?

c. Will carbon burn? How do you know?

3. State three characteristics of carbon (charcoal) that you have learned from these experiments.

4. Hold your hand over the glowing charcoal with your eyes closed. How can you still tell that the carbon is burning?

10. Oxygen (symbol, O). - Laboratory Study No. 2. Demonstration.

Preparation of oxygen: Thoroughly mix a teaspoonful of potassium chlorate with about one-fourth as much black oxid of manganese. Put the mixture in a large test tube. Close the mouth of the test tube with a stopper through which passes a delivery tube, the other end of which runs beneath the surface of water in a tray. Support the test tube in a slanting position on an apparatus stand, and heat the mixture gently with a gas or an alcohol flame, until