that is proportioned to the quantity of tissues burned, to the amount of oxygen consumed in the acts of vital chemistry that constitute nutrition. It is possible to reach a considerable sum of daily work without at any moment making intense exertion or rapid movements. The muscular acts of exercises chosen have for that only to be continued long, without being very violent or very rapid. In other words, it is enough that the exercise represents "bottom" work.
Walking is the type of "bottom" exercise, and is the most hygienic of all kinds for the elderly man, provided it is prolonged enough to represent a sufficient amount of work. Nothing is so good for the man of fifty years as a gunning tramp, or long pedestrian tours like those the Alpinists make. But it is necessary to regard the social exigencies, which refuse to give everybody the desired number of hours, and compel another choice. There are many other "bottom" exercises that exact a larger expenditure of force than walking, without going beyond the degree of effort and rapidity that the arteries of the elderly man can safely bear. Many of what are called open-air games, like tennis, lawn-tennis, and even rowing, when practiced not for racing but as a recreation—that is, with a liveliness graduated to the respiratory capacity of the rower—provoke, for example, in one or two hours, an elimination of the products of disassimilation and an acquisition of oxygen equivalent to what one can get from eight or ten hours of walking. They permit the busy man to gain time, compensating for the shorter duration of the exercise by its intensity; but that in such a way that he can get the general consecutive effects of exercise while avoiding its general immediate effects, super-activity of the circulation of the blood and of respiration.
We ought to look also to exercise for local effects; in order, in the first place, to keep the joints supple and counterbalance the tendency to incrustation of the cartilages, which is one of the consequences of age; and, in the second place, to keep the muscles as a whole in sufficient strength and volume. The muscle, as we have read, is "the furnace of vital combustion," and in developing the muscular tissue we favor the activity of combustion and the destruction of the refuse of nutrition. For the satisfaction of these requisitions, such exercises are adopted as might be called analytical, inasmuch as they bring the whole muscular system into play, not by the work of the whole together, but by a series of successive movements that call the various muscular groups into action severally one after the other. It is important, in order to preserve the easy working and suppleness of all the articulations of the body, to subject them to movements extending to the extreme limit of possible displacement. We might also,
