Again, exercise stimulates and strengthens the organs of digestion.  The appetite is improved, as is especially noted after exercise in the open air.  The digestion is more complete, absorption becomes more rapid, the peristaltic movements of the bowels are promoted, and the circulation through the liver is more vigorous.  More food is taken to supply the force necessary for the maintenance of the mechanical movements.  Ample exercise also checks the tendency towards a torpid circulation in the larger digestive organs, as the stomach and the liver, so common with those who eat heartily, but lead sedentary lives.  In short, exercise may be regarded as a great regulator of nutrition.

Exercise increases the flow of blood through the small vessels of the skin, and thus increases the radiation of heat from the surface.  If the exercise be vigorous and the weather hot, a profuse sweat ensues, the rapid evaporation of which cools the body.  The skin is thus a most important regulator of the bodily temperature, and prevents any rise above the normal which would otherwise result from vigorous exercise. (See secs. 226 and 241).

84.  Effect of Exercise upon the Personal Appearance.  Judicious and systematic exercise, if moderately employed, soon gives a more upright and symmetrical figure, and an easier and more graceful carriage.  Rounded shoulders become square, the awkward gait disappears, and there is seen a graceful poise to the head and a bearing of the body which mark those whose muscles have been well trained.  A perfectly formed skeleton and well-developed muscles give the graceful contour and perfect outline to the human body.  The lean, soft limbs of those who have never had any physical education, often look as if they belonged to persons recovering from sickness.  The effects of sound physical exercise are well exhibited in the aspect of the neck, shoulders, and chest of one who has been well trained.  This is noticeable in gymnasts and others who practice upon the horizontal bar, with chest weights, dumb-bells, and other apparatus which develop more especially the muscles of the upper half of the trunk.

[Illustration:  Fig. 41.—­Young Woman practicing at Home with the “Whitely Exerciser.” (From a photograph)]

Exercise improves the condition of the tissues generally.  They become more elastic, and in all respects sounder.  The skin becomes firm, clear, and wholesome.  Hence, every part of the surface of the body rapidly takes on a change in contour, and soon assumes that appearance of vigor and soundness which marks those of firm physical condition.  The delicate, ruddy aspect of the complexion, the swing about the body and the bearing of the head and shoulders, of young women whose physical training has been efficient, are in marked contrast with those characteristics in persons whose education in this respect has been neglected.

85.  Effect of Unsuitable or Excessive Exercise.  But exercise, like everything else which contributes to our welfare, may be carried to excess.  The words excessive and unsuitable, when applied to muscular exertion, are relative terms, and apply to the individual rather than to amount of work done.  Thus what may be excessive for one person, might be suitable and beneficial to another.  Then the condition of the individual, rather than the character of the muscular work, is always a most important factor.