Lastly, let it be carefully observed, such a belief as this as to the origin of life, and of the basis of all life in chemical processes, carries with it no necessary adherence to the doctrines of Materialism. The materialist analyses the whole objective world of phenomena into matter and motion. So far, his conclusion is perfectly legitimate; but when he maintains that matter and motion are the only realities of the world, he is making an unwarrantable assumption. Matter in motion is accompanied by consciousness in ourselves. We infer a similar consciousness in creatures like ourselves. As the movements and the matter differ from those that occur within our body, so will the accompanying consciousness. The simplest state of affairs or "body" we can imagine is that of a gas such as hydrogen. But such a simple state of matter may have its accompanying consciousness, as different from ours as is the structure of our bodies from that of a hydrogen molecule. This is, of course, also an assumption, but it is one that harmonises with the facts of experience.

The opposite extreme to Materialism is Idealism, and in this school of philosophy an assumption precisely similar, and exactly opposite to that of Materialism, is made. The idealist says the objective world of phenomena has no existence at all, it is the creation of mind. An objection to such a theory lies in the question, If matter and energy are the creation of mind, how is it that we find them to be indestructible?

Popular philosophy has made an assumption which lies midway between these extremes. It postulates two realities, matter and spirit, having little effect upon one another, but acting harmoniously together.

But the view that is here set forth postulates neither matter nor spirit, but an entity which is known objectively as matter and energy, and subjectively as consciousness. This philosophy goes by the name of Monism. The term consciousness is used for lack of any other to express the constant subjective reality. Carefully speaking, it is, of course, only the more complex subjective processes that form consciousness.

CHAPTER IX

THE DIVIDED LABOURS OF THE BODY

1. Division of Labour-2. The Functions of the Body: Movement; Nutrition; Digestion; Absorption; The Work of the Liver and the Kidneys; Respiration; Circulation; The Changes within the Cells; The Activities of the Nervous System3. Sketch of Psychology

1. Division of Labour,-The simplest animals are onecelled; the higher animals are built up of numberless cells. All the processes of life go on within a single cell. In a many-celled animal the labours of life are divided among the various groups of cells which form tissues and organs. The history of physiological development is the history of this division of labour.

When a dividing cell, instead of separating into two distinct masses, remained, after the division of its nucleus, with the two daughter masses lying side by side, joined together by strands of protoplasm, then the evolution of organic form took a distinct step upwards, and at the same time arose the possibility of greater activity, by means of the division of labour. For when the process had resulted in the formation of an organism of a few dozen cells, arranged very likely in the form of a cup, the outer cells might devote the greater part of their energies to movement and the inner cells to the digestion of food. In the common Hydra the body consists of two layers of cells arranged to form a tube, the mouth of which is encircled by tentacles.

The cells of the outer layer are protective, nervous, and muscular; the cells of the inner layer are digestive and muscular. The cells of Hydra are therefore not so manysided in function as are Amabæ. In animals higher than the simplest worms, a middle layer of cells is always formed which discharges muscular, supporting, and other functions.

With advancing complexity of structure the specialisation of certain cells for the performance of certain functions has become more pronounced. In the human body the division of labour has reached a state of great perfection; we shall give a slight sketch of its arrangements.

2. The Functions of the Body.-Our objective life consists of movement, and of feeding to supply the energy for that movement. Growth, reproduction, and decay are elsewhere treated of.

Movement. We move by the contraction of cells massed into tissues called muscles. Contractility is a property of all living matter; in muscle-cells this function is predominant. This is all that need be said here of movement; the processes of nutrition we must follow more closely.

Nutrition. All the cells of our bodies are nourished by the stream of fluid food-stuff, the blood, which flows in a number of vessels called arteries, veins, or capillaries, according to their place in the system. From this stream each cell picks out its food; and into another streamthe lymph stream-moving in separate channels — the lymphatics, which, however, join the blood channels, each cell casts its waste material; just as a single-celled animal takes food from the water in which it lives and casts its waste into it.

Nutrition must therefore consist of two series of activities. One series will have for its object the preparation of food-matter so that it may enter the blood, and the excretion of waste products out of the blood. The other series will consist of the activities of the individual cells,— the manner in which they feed themselves.

The first step in the preparation of the blood is digestion. Most food-stuff is solid and indiffusible; before it can enter the blood it must be made soluble and diffusible. The

supply of oxygen to the tissues is also a part of these first processes of nutrition. Being a gas, it is treated in a special way which will be described immediately.

Digestion. The various food-stuffs have various chemical qualities. After being swallowed they enter a long tube, the digestive tract or alimentary canal. Within this canal they are subjected to the action of various digestive juices prepared by masses of cells called glands. Saliva is one of these juices, gastric juice is another, pancreatic juice is another. The effect of these juices upon the food is that most of it is dissolved in the juice and made diffusible. Thus we see an example of the division of labour. An amoeba flows round a solid particle of food and digests it. In the higher animals the cells of the digestive glands are specialised for this particular function and do little else.

Absorption. After the food is digested it leaves the alimentary canal, and is absorbed into the blood-vessels and lymphatics in the walls of the canal. Absorption is not a mere process of diffusion. It is diffusion modified by the cells lining the alimentary tract. Certain chemical changes are effected at the same time. Most of the absorbed food passes to the liver; but the fat does not go directly into the blood, being first absorbed into that other system of vessels, the lymphatics. Eventually it also gets into the blood; for the two streams are connected.

The Work of the Liver and the Kidneys.-The cells of the liver secrete a juice called bile, which is poured into the alimentary canal. The exact function of this juice is still doubtful. It has a certain use in the digestion of fats, but it is largely an excretion. The stream of food-stuff going to the liver contains sugar, the result of the digestion of carbohydrates; albumen, the result of the digestion and absorption of proteids; and certain waste nitrogenous matters formed during the digestion of proteids.

The cells of the liver retain the sugar, store it within themselves, in the same sort of way that a potato stores up starch, and give it up gradually to the blood again. So far as is known they do not affect the albumen in any way,

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but the waste nitrogenous matter is altered and then sent on in the blood stream to the kidneys.

The cells of the kidneys take this stuff, which was prepared in the liver, and other waste nitrogenous products out of the blood, pass them and a certain amount of water along to the urinary bladder, which empties itself from time to time.

Respiration.—Breathing consists of two distinct acts, inspiration and expiration. During an inspiration air is drawn into lungs. Thence the oxygen passes by diffusion, modified by the fact that the essential membrane is a living one, into the blood. There it enters into a loose combination with hæmoglobin, the red colouring matter of the blood cells, and is thus carried to the cells of the tissues to be absorbed into their living matter. During an expiration we breathe out air which has less oxygen and more carbonic acid gas than normal air. The carbonic acid is a wasteproduct formed by the cells of the body; it first enters the blood, is then carried to the lungs, and leaves the bloodvessels by a process of diffusion similar to that by which the oxygen entered. The close association of these two processes is simply due to the fact that an organ fitted for the diffusion of one gas in one direction will do for the diffusion of all gases in any direction.

Circulation. The blood is maintained in a healthy state by the processes we have described. By the active contraction of the heart it is pumped round and round the body, continually carrying with it fresh food to the tissues, and carrying away with it the waste matter cast out of the tissues. All the blood-vessels, except the very smallest, have muscular walls. The heart is a large hollow mass of muscles, is a part of a pair of large blood-vessels that have been bent upon themselves, and arranged so as to form four separate chambers, two upper and two lower, an upper and a lower opening directly into one another on each side. By the contraction of the lower chamber of the left pair the blood is forced through all the vessels of the body; these collect and empty the blood into the upper chamber of the right pair; from this it passes into the lower chamber on