every kind of excess, all violent and unpleasant emotion, all mental
overstrain, take daily exercise in the open air, cold baths and such
like hygienic measures. For without a proper amount of daily exercise
no one can remain healthy; all the processes of life demand exercise
for the due performance of their functions, exercise not only of the
parts more immediately concerned, but also of the whole body. For, as
Aristotle rightly says, _Life is movement_; it is its very essence.
Ceaseless and rapid motion goes on in every part of the organism.
The heart, with its complicated double systole and diastole, beats
strongly and untiringly; with twenty-eight beats it has to drive the
whole of the blood through arteries, veins and capillaries; the lungs
pump like a steam-engine, without intermission; the intestines are
always in peristaltic action; the glands are all constantly absorbing
and secreting; even the brain has a double motion of its own, with
every beat of the pulse and every breath we draw. When people can get
no exercise at all, as is the case with the countless numbers who
are condemned to a sedentary life, there is a glaring and fatal
disproportion between outward inactivity and inner tumult. For this
ceaseless internal motion requires some external counterpart, and the
want of it produces effects like those of emotion which we are obliged
to suppress. Even trees must be shaken by the wind, if they are to
thrive. The rule which finds its application here may be most briefly
expressed in Latin: _omnis motus, quo celerior, eo magis motus_.

How much our happiness depends upon our spirits, and these again upon
our state of health, may be seen by comparing the influence which the
same external circumstances or events have upon us when we are well
and strong with the effects which they have when we are depressed and
troubled with ill-health. It is not what things are objectively and in
themselves, but what they are for us, in our way of looking at them,