Three principal points in the manner of taking exercise are necessary to be attended to: - 1. The kind of exercise. 2. The proper time for exercise. 3. The duration of it. With respect to the kinds of exercise, the various species of it may be divided into active and passive. Among the first, which admit of being considerably diversified, may be enumerated walking, running, leaping, swimming, riding, fencing, the military exercise, different sorts of athletic games, etc. Among the latter, or passive kinds of exercise, may be comprised riding in a carriage, sailing, friction, swinging, etc.

660. The First, or active exercises are more beneficial to youth, to the middle-aged, to the robust in general and particularly to the corpulent and the plethoric.

661. The Second, or passive kino's of exercise, on the contrary, are better calculated for children; old, dry, and emaciated persons of a delicate and de-bilitated constitution; and particularly to the asthmatic and consumptive.

G62. The Time at which exercise is most proper, depends on such a variety of concurrent circumstances, that it does not admit of being regulated by any general rules, and must therefore be collected from the observations made on the effects of air, food, drink, etc.

663. With respect to the duration of exercise, there are other particulars, relative to a greater or less degree of fatigue attending the different species and utility of it in certain states of the mind and body, which must determine this consideration as well as the preceding.

664. That exercise is to be preferred which, with a view to brace and strengthen the body, we are most accustomed to, as any unusual one may be attended with a contrary effect.

660. Exercise should be begun and finished gradually, never abruptly.

666. Exercise in the open air has many advantages over that used within doors.

667. To continue exercise until a profuse perspiration or a great degree of weariness takes place, is far from being wholesome.

668. In the forenoon, when the stomach is not too much distended, muscular motion is both agreeable and healthful; it strengthens digestion, and heats the body less than with a full stomach; and a good appetite after it is a proof that it has not been carried to excess.

669. But, at the same time, it should be understood, that it is not advisable to take violent exercise immediately before a meal, as digestion might thereby be retarded.

670. Neither should we sit down to a substantial dinner or supper immediately on returning from a fatiguing walk, at a time when the blood is heated, and the body in a state of perspiration from previous exertion, as the worst consequences may arise, especially where cooling dishes, salad, or a glass of cold drink is begun with.

671. Exercise is always hurtful after meals from it* impeding digestion, by propelling those fluids too much towards the surface of the body which are designed for the solution of the food in the stomach.