ion: Fig. 40.--The Standard Special Chest Weight.

A convenient machine by means of which all the muscles of the body may be
easily and pleasantly exercised with sufficient variations in the
movements to relieve it of monotony.

A space 6 ft wide, 6 ft deep, and 7 ft high nearly in front of the machine
is required for exercise.]

In time, however, acts which were first done only with effort and by a
conscious will, become automatic. The will ceases to concern itself. By
what is called reflex action, memory is developed in the spinal cord and
the muscular centers (sec. 273). There is thus a great saving of actual
brain work, and one important cause of fatigue is removed.

83. Effect of Exercise on Important Organs. The importance of
regular exercise is best understood by noting its effects upon the
principal organs of the body. As the action of the heart is increased both
in force and frequency during exercise, the flow of blood throughout the
body is augmented. This results from the force of the muscular
contractions which play their part in pressing the blood in the veins
onward towards the heart. Exercise also induces a more vigorous
respiration, and under increased breathing efforts the lung capacity is
increased and the size of the chest is enlarged. The amount of air
inspired and expired in a given time is much larger than if the body were
at rest. The blood is thus supplied with a much larger amount of oxygen
from the air inhaled, and gives off to the air a corresponding excess of
carbon dioxid and water.

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