This section is from the book "Human Physiology For The Use Of Elementary Schools", by Charles Alfred Lee. Also available from Amazon: Human Physiology, for the Use of Elementary Schools.
1. Physiology is " the science of life," or that branch of knowledge which explains the uses of the various organs of living beings. Vegetable physiology treats of the functions of plants ; and Comparative physiology, of those of the inferior orders of animals ; while Human physiology treats exclusively of man.
2. The kingdom of nature embraces three great classes, animals, vegetables, and minerals. According to a more scientific arrangement, it is composed of organic and inorganic bodies. By organic bodies, we mean those which possess organs or instruments for the performance of certain functions ; and by inorganic, those which do not. It is by a knowledge of these works of God, that we derive our ideas of his power, wisdom, and goodness.
3. Organized bodies are divided into two great classes, animals and vegetables ; which differ from inorganic matter in several respects, the most important of which are the following :-
4. Organized bodies have a certain determinate form, peculiar to the species to which they belong. Every species of plant or animal may be known by its external shape ; as a horse, a cow, a tree, or a rose. They differ so much from all other kinds, that we are seldom in danger of mistaking them. This will not apply to inorganic bodies, except, perhaps, to a few minerals which crystallize in a certain shape.
5. In organized bodies, we find the parts of which they are composed, distinguished by round or oval forms ; as the body and leaves of trees; the petals of flowers ; the bodies and limbs of animals. We scarcely ever see straight lines, or sharp angles among them, as in mineral substances.
Every species of animal or vegetable has its own proper size, from which it varies but little. But minerals may be large or small; the substance called granite, for example, may make a pebble or a mountain.
6. Inorganic bodies contain either a single element, as carbon, sulphur, etc, or several of the elementary or simple substances, which are fifty two in number, as lime, silex, and magnesia ; while in organized bodies, we find at least three of these elements, as carbon, hydrogen, and oxygen in vegetables ; and the same, with the addition of azote or nitragen in animals. In organic bodies, there have been discovered in all eighteen simple substances, though they generally contain but three or four.
7. But these two classes of substances, not only differ as to the number of the elements which enter into their composition, they also differ, as to the mode in which these elements are combined. Thus in minerals, two elementary substances unite and form a compound, and this again, combines either with another simple substance, or with a compound composed of two other simple substances. Thus, for example, carbonate of ammonia is composed of carbon, oxygen, hydrogen, and nitrogen, but combined as follows :-
The carbon and oxygen unite to form carbonic acid ; the hydrogen and nitrogen, to form ammonia; these two compounds thus uniting, form carbonate of ammonia.
In animals, we find the same simple elements uniting, each with all the others, forming the peculiar principles of organic bodies, such as fibrin, gelatine, etc.
8. Organized bodies contain small particles of matter of a round or oval shape, both among their solid and fluid parts. These are supposed, according to their different arrangement, to make up all the elementary forms of organized bodies ; as when arranged in lines, they form nerves, tendons, and muscles ; in sheets, the various membranes and coats of vessels ; and in masses, the solid substance of the glands, as the liver, kidneys, and pancreas.
9. There are but few changes in inorganic bodies. The elements of which they are composed remain at rest. Rocks and mountains are the same now, as they were five thousand years ago. But in organized bodies, compounds are continually forming to be again separated ; animals feed on vegetables, and vegetables on animals.; " See dying vegetables life sustain; See life dissolving, vegetate again ; All forms that perish, other forms supply- By turns we catch the vital breath and die."
10. In organized bodies the parts are mutually dependent on each other for support. If we cut off the limb of a tree, it dies, because it can receive no sap ; if we amputate a finger, it mortifies, because the circulation of the blood has ceased ; but if we break off a piece of marble, it will remain unchanged as long as the original mass.
11. Inorganic substances exist either in solid, liquid, or gaseous forms. They are wholly solid, liquid, or gaseous. But organic matter always presents a combination of solid and fluid parts. We find fluids circulating in regular vessels, and the solids and fluids mutually dependent on each other for support. In vegetables, we discover various parts, such as wood, bark, leaves, roots, and flowers; and in animals, muscles, nerves, tendons, vessels-all of which are organs, or instruments for the accomplishment of certain purposes. Inorganic bodies are formed of homogeneous parts, or parts perfectly similar.
12. Organic bodies are composed of two kinds of elements, chemical, such as oxygen, carbon, and hydrogen, which exist in minerals ; and organic, or proximate, such as albumen, gelatine, fibrin, etc, such as are never found in inorganic matter. It is because these organic substances are produced by the peculiar forces of organic life, and not by chemical laws, that we cannot decompose and then re form them, out of the same elements, as we can minerals. For example, we can dissolve alum, salt, or copperas, and then by evaporation, crystalize them in the same shape again.
13. The general properties of organic or inorganic bodies differ in many particulars. In the first place there is a constant warfare going on, between the chemical and physical laws, which govern inorganic matter, and the vital laws which maintain animal life. This conflict commences at the first period of our existence, and is kept up to the moment of our dissolution. Life is enabled, for wise purposes, to wrest portions of matter from the domain of the laws of matter, for a certain indefinite period ; for a while, the vital powers maintain a successful contest, but at last they have to yield, and death gives over the body to the action of the chemical forces.