strap. A weight should be
distributed over a set of muscles as evenly as possible, and this is the
reason for suspending a knapsack from two shoulders instead of one, when
possible.

Finally, in doing any sort of lifting or pulling, if the muscles that
are to be used are contracted before grasping the weight they will be
able to do their work with far less effort. Try lifting a small weight
like a book in two ways--first, have your hand and fingers relaxed and
limp when you grasp it, and see how heavy it seems and how hard it is to
contract your muscles properly while lifting it. Then drop the book and
go at it again, this time anticipating its weight and contracting your
hand and finger muscles before grasping it. See how easily it comes up.
Try this same thing with heavier weights, and learn _always to contract
the muscle before taking the load_. In carrying a weight for any
distance it is well to shift it from one arm to another, always
preparing the muscles by contracting them before the weight is assumed.

Using the muscles so as to take advantage of their lever-like qualities
in the best way, contracting them before loading, and pushing instead of
pulling, go to make up what is sometimes called "getting a purchase."

4. _Supply Daily Need for Air, Sun, Water and Food_--Besides exercise
and rest there are other controllable factors upon which health depends.
These are air, heat and light of the sun, water and food. To grow and
work properly the body needs plenty of each of these.

_Air_--If you cannot work or play outdoors you can still bring out of
doors in by opening your windows at frequent intervals. You will find
that work goes better, and that you do not tire so easily if you make it
a rule to open the windows and doors and move about the room for five
minutes every hour or two. Sleep with windows open or out-of-doors. Camp
and hike as often as possible. Work in the garden. Play out-of-door
games.

_Heat_--The proper temperature of the body is between 98 and 99 degrees
Fahrenheit. Human life depends upon the maintenance of this temperature
at all times, and very slight changes either up or down interfere
seriously with all the other life processes. The main source of heat is
from food consumed, or really burned, in the body. Artificial heating in
houses helps conserve the body heat, as does clothing. But clothes and
shelter may make you overheated, which is nearly as bad as being cold;
they may also shu