This comes last alphabetically of the five essentials concerned in the maintenance of health - namely, ablution : the skin and the bath; bed-room ventilation; clothing; diet; and exercise - but it is none the less important on that account. Exercise may be defined as action of the body, whereby its organs and their functions are kept in a state of health. Each one of us has from the moment of his existence a certain stature allotted, as it were, to which he will attain. In this way some will be tall, others will be short, so that the height of the body is something quite beyond our control, as we know by the interrogation, "Which of you by taking thought can add one cubit to his stature ?" But in contradistinction to height, we know that the muscles of the body can be developed and increased in size by use. It is by their action in exercise that the muscles are enlarged, hardened, and brought to their greatest state of perfection. And it is only by exercise, and by exercise alone, that they can be maintained at the acme of physical condition.

Now, in the same way that education develops and increases the power of the brain, so exercise has a similar effect on the body. When the muscles are strengthened, the beneficial effect is also participated in by the heart, lungs, and digestive organs, and thus the removal of worn-out material from the body is assisted. The effect of exercise is thus to remove used up products from the system, and so afford an opportunity for renewed material to take their place. Ceaseless changes are constantly going on throughout the body, and any part which has fulfilled its object is no longer necessary for the requirements of the system, in fact it becomes injurious. Its removal has to take place by one of the various outlets, and it is by exercise that its expulsion is greatly assisted. In this way exercise differs altogether from the part played by food. The latter is the introduction of nourishment into the system for the renewal of its wants, while exercise is the principal agent by which debris is eliminated.

It was well known amongst the Greeks and Romans that the muscles reached their greatest state of development by means of exercise. Though, therefore, gymnastics formed a great part of their system of education, yet the chief aim in their athletic instruction was the desire to train men to fight their battles, and in those days war was a matter of personal valour and of individual bravery. On that account, therefore, the men who were selected as their soldiers were among the healthiest of the nation. Those who by reason of bodily infirmity or inherent weakness were unfitted for military prowess were left alone. But, as Maclaren has well pointed out, the object of systematic and proper exercise is not for the production of a race of soldiers, though a certain proportion of the population will always be required for military service. With the great majority of men the struggle for existence is keen, and it is simply a question of the survival of the fittest, and of the weakest going to the wall. The requirements of the present time are therefore a capacity for endurance and an ability to withstand the effects of work day after day. We do not require athletes who are capable of performing wonderful feats of strength; but the fight of the nineteenth century is brain against brain, and he will be best equipped for the struggle who has the advantage of good bodily health. In the higher callings, where brain power is everything, the necessity for perfect physical condition is all the more imperative, because the brain is supplied with healthy blood, and the ideas flow with less effort.

The brain is an organ of the body exactly in the same way that the heart, the lungs, and the liver are, and therefore is subject to the same changes which belong to every other part of the frame. It will be at its best when there is circulating through it a full supply of rich red arterial blood, for that means a continual renewal of fresh material to it, and a speedy removal of worn-out products. It is by exercise mainly, whether it be voluntarily undertaken, or whether it pertain to the calling, that the body is kept at the pink of condition, and the brain benefited accordingly. Another greai and important result from improving the bodily health is the increased power of what we call the will. The undertaking, say, of a long walk or climb involves the possession of a certain amount of determination, and many people, though perfectly aware of. the good to be obtained by a few hours' exercise outside the house, have not the determination to carry it into effect. Once the disinclination to move is overcome, the effort required is less each time, and ultimately the will gains a distinct mastery.

When the muscles are put into action, what is termed their contractility is called into play - that is, the force which was dormant before is roused into activity. This is effected through the nervous system, and it is the will which emanates from the brain and is carried along certain nerves to accomplish definite actions. During the contraction of a muscle its individual fibres change in form, producing an alteration in the shape of the whole muscle; thus it becomes shorter and thicker. At the same time, while it is in action more blood flows through it, hence we see that one of the beneficial effects of exercise is to stimulate the circulation through the muscular system. It has also been ascertained by experiments, that the venous blood which comes from a muscle in action is darker in colour than that from a muscle in repose. When the circulation is quickened by movement, and the blood stream hastened, the vigour of the body is increased, because the used up material is all the quicker taken away, and a freshly created supply of nutrition brought to every part.

The rate of breathing is accelerated whenever the body is engaged in muscular exertion, and with this quickened breathing there is an increased amount of oxygen drawn in, and an increased amount of carbonic acid gas and water exhaled by the breath. The oxygen which is absorbed from the air into the blood is stored in the red corpuscles of the latter, by which it is carried to every part of the body. The venous blood which returns from every portion of the system comes back as a dark crimson, instead of being bright scarlet like the arterial blood. It contains carbonic acid, and returns it to the lungs, where it is exhaled by the breath. The oxygen is necessary to existence, while the carbonic acid is injurious. The effect of exercise, then, in any form, is thus to distribute healthy blood more rapidly through the system, while it removes the injurious matters quite as speedily.