in amongst it, and, mixing with it, turns it into the chyle or which I have just spoken.

This chyle owes its white colour to countless minute fatty particles mixed up with it, as oil is in an emulsion. It is forced along the small intestine by peculiar movements of the bowels, called the peristaltic * motions, which are a succession of contractings and relaxings, by which the different portions of the bowels rise and fall in turn, like the motions of a worm or snake. As it is thus being thrust onwards, the dissolved matter it contains is absorbed by the glands of the villi, while the fatty particles pass through the villi into the vessels within, just as the air passes through the walls of the air-cells in the lungs. The blood-vessels and the lacteals, between them, thus finally absorb into the blood all the nutritious part of our food, and leave only what is of no use for the support of the system to pass off into the larger intestine.

MUSCLES AND NERVES.

1. The muscles form the greater part of the flesh of men and animals, and supply them with the power of moving, and thus of using their various limbs and organs. It is by the help of muscles that our hearts beat and that our limbs are at our service: they are at work for us, incessantly, in carrying on the countless internal movements of our system necessary for life, and we call multitudes of them into play by the minutest external motion of the body or of any of its parts.

2. The muscles are of very various forms, according to their special use, and the shape and position of the bones on which they are fixed, and which they have

to move.

Their colour is deep red in beef and mutton, and in human flesh, but semi-transparent, grey, or whitish in animals newly born, as, for example, in veal; and they are of the same pale colour in fish, the rabbit, &c.

The larger or slighter swellings under the skin by which we judge the strength of wrestlers and other athletes, or that of ordinary men, are caused by the muscles. Weakness is shown by their smallness; power by their being large and prominent. It is the muscles and their tendons-that is the prolongations of their substance by which they are united to the bones,-which many speak of as the nerves.

Fig. 28.

B.

A

3. The muscles consist of bundles of parallel fibres (Fig. 28) which possess the power of contracting themselves, and thus

* From Greek peristello, to contract; or peristalto, to surround.

of shortening and thickening their substance, when they draw their ends, fixed on the bones, nearer each other.

The muscular fibres, B, are long and cylindrical, and are crossed by what are called striæ,* A, which are parallel to each other, and may be seen, under the microscope, approaching each other when a muscle is contracting.

These fibres pass, at their two ends, into the fibrous substance of the tendons, and they are sheathed in membranous tissue, which separates them from other fibres around. They are further united into bundles, and several of these together form a muscle, which, itself, is sheathed in fibrous tissue, and ends, at its extremities, in tendons, fixed to the bones. The whole muscle decreases in length, and approaches the points at which it is fixed to the bones, during its contraction.

4. This muscular contraction takes place by the influence of the will on the muscles of the limbs, and by that of the nervous system, without any action of the will, in the muscles of the heart and those of the vital organs.

5

er

Fig. 29.

The muscles are connected with the cells of the brain and of the spinal marrow, by the nerves. The threads of the motive nerves -that is of those by which motion is brought about-pass into a cell of the grey outer substance of the spinal marrow, while the other end joins the muscular fibre by a small swelling, in the way shown in Fig. 29.

5. The nervous influence emanating from the brain and the spinal marrow passes through the nervous cord, as the electric spark passes through the wire of the telegraph. It flashes along the threads of which the cord is composed to the raised point at which it is joined to the muscle, and instantly contracts it. Electricity applied, either directly to a muscle or to the nerve connected with it, produces the same contraction.

In this contraction, all the fibres in the various fibrous bundles of which the muscle consists, act at once, diminishing its length and causing a quick movement by which its extremities, joined to the bones, are brought closer together. Most of the motions of our limbs require the simultaneous contraction of a number of muscles. The quickness and exactness of these movements is amazing. A violin-player bends his fingers forty or fifty times in a second, pressing on the string, each time, with just the force required. Even this, however, is nothing compared with the rapidity of muscular motions in some of the lower animals, for the

* A Latin word meaning a groove, furrow, or crease.

muscles of the wings of a commor fly contract about four thousand times in a second, when it is darting through the air at its swiftest.

6. You may yourself feel the contraction of your own muscles by grasping the upper part of your right arm with your left hand, and then bending the right arm together. The muscles of the upper arm will be felt and seen to swell and stiffen. In the case of men who use their arms much in their occupations-as, for instance, blacksmiths or sailors, this is very noticeable.

During the action of the muscles various chemical phenomena take place in their substance. The blood enters it in great abundance, and the organic matter of which the blood consists suffers combustion by oxygen more freely than when we are at rest. The heat, which is, really, combustion, or, in other words, the union of oxygen with the organic matter of the blood, increases; carbonic acid is formed in great abundance, and what is called lactic acid is also produced. It is the accumulation of these materials, resulting from combustion, which in the end, by obstructing the action of the muscle, and rendering contraction more and more painful and difficult, causes the sensation of fatigue, and forces us to rest after prolonged toil.

THE NERVES.

1. The nerves are white cords which go out from the brain and the spinal marrow, and divide themselves through, the body, so as to reach every part of it. There are two great classes of them.

First. Those which transmit impressions received from without to the central nervous organ, the brain. They are called the SENSORY,* or AFFERENT† NERVES, because they are the agents of the senses, and carry their messages to the brain.

Second. The second class is the MOTOR, or EFFERENT § NERVES, which get their name from being the cause of motion, and the agents in carrying out the messages of the brain to the muscles.

2. The great majority, if not the whole of the movements of the body and of its parts, are the effects of some influence applied to the outer ends of the different nerves, and transmitted through them to the brain, or the central nervous organ with which they are connected. Having thus delivered their message, a further influence is then sent out through the efferent or motor nerves, from the central organ to the muscles affected, and this causes their particles to take up a new position, so that each fibre becomes shorter and thicker.

3. Thus the sensory, or afferent nerves—or, as they are sometimes called, the nerves of sensibility—transmit the impressions of the senses to

* From Latin sensus, a sense, which is formed from sentio, sensum, to feel, to perceive. From Latin affero, to bring, to carry.

From Latin moveo, motum, to move.
From Latin effero, to carry forth.

the brain, and the brain then sends out. its commands, in obedience to these, to the muscles of voluntary motion*-that is, to the muscles which are moved by the power of the will. The central organ of the nervous system, the brain, when altered by disease, can neither receive nor transmit the impulses of feeling or motion. If it be injured on one side, this will be seen by the paralysis of one side of the body; but as the nerves cross before entering the brain, it is the opposite side of the body, not the side on which the brain is affected, which is paralysed.

4. The sense of touch is due to the presence in every part of the skin, of countless minute nerves. They run below the little ridges or rough

Fig. 30.

nesses of the outer skin, and have their termination in the true skin which underlies the outer, insensible, epidermis. † These roughnesses are caused by what are called papilla, which are rows of little eminences formed by loops of a very fine nerve and artery. They are protected from injury by deadens the effect of

the outer skin, which does not feel, and thus contact with anything external. The papillæ are larger in those parts where the sense of touch is most delicate, and consist of a number of branch nerves and arteries of almost inconceivable fineness. The epidermis does not follow the undulations of these little bodies, but is spread smoothly over them, and hence they come near the surface over the whole body, like little peaks rising upwards, nearly through a liquid. The sense of touch is caused by thousands of these minute points coming in contact with an object, and sending their sensations to the brain. How extremely sensitive they are is seen in the fact that their mere exposure tc the air, by the removal of the cuticle, or epidermis, causes pain.

* Latin voluntarius, from volo, to will.

The outer skin, which is épi tó dermati, over the true skin.
Papilla (Latin), a nipple-any little lump.

THE BRIDGE OF SIGHS.-Thomas Hood.

"Drown'd! Drown'd!"-Hamlet.