exercise _in the open air_, till a
slight degree of fatigue be felt; then to rest one hour, and breakfast.
After this rest three hours, "in order that the energies of the
constitution may be concentrated in the work of digestion;" then take
active exercise again for two hours, rest one, and then dine. After dinner
rest for three hours; and afterwards, in summer, take a gentle stroll,
which, with an hour's rest before supper, will constitute the plan of
exercise for the day. In wet or inclement weather, the exercise may be
taken in the house, the windows being opened, "by walking actively
backwards and forwards, as sailors do on ship-board."

We now come to the consideration of _air_. Pure air is as necessary to
existence as good and wholesome food; perhaps more so; for our food has to
undergo a very elaborate change before it is introduced into the mass of
circulating blood, while the air is received at once into the lungs, and
comes into immediate contact with the blood in that important organ. The
effect of the air upon the blood is this: by thrusting out as it were, all
the noxious properties which it has collected in its passage through the
body, it endues it with the peculiar property of vitality, that is, it
enables it to build up, repair, and excite the different functions and
organs of the body. If therefore this air, which we inhale every instant,
be not pure, the whole mass of blood is very soon contaminated, and the
frame, in some part or other speedily experiences the bad effects. This
will explain to us the almost miraculous benefits which are obtained by
_change of air_, as well as the decided advantages of a free and copious
ventilation. The prejudices against a free circulation of air, especially
in the sick chamber, are productive of great evil. The rule as regards
this is plain and simple: admit as much fresh air as you can; provided it
does not _blow in_ upon you _in a stream_, and provided you are not in a
state of profuse perspiration at the time; for in accordance with the
Spanish proverb--

"If the wind blows on you through a hole
Make your will, and take care of your soul."

but if the _whole of the body be exposed at once_ to a cold atmosphere,
no bad consequences need be anticipated.

A great deal has been said about the necessary quantity of _sleep;_ that
is, how long one ought to indulge in sleeping. This question, like many
others, cannot be reduced to mathematical precision; for