, rest and sleep is concerned, the
rule to follow is obviously this: _Determine accurately by experiment
the proper relation between periods of work and periods of rest in
your own case, then increase your efficiency by maintaining this
relation_.

In Denmark they feed cows scientifically. Day by day they increase
the allowance of milk-producing food. Day by day the yield of milk
increases. At last there comes a day when measurement shows that there
is no longer any increase in the production of milk. They then
decrease the food till the output of milk diminishes. So they
determine the normal.

So with you and your hours of work and leisure. Give more and more
time to your business each day until there comes an impairment in the
quality of your work. Stop short of this. You have found your norm of
efficiency.

CHAPTER V

THE SECRET OF MENTAL EFFICIENCY

[Sidenote: Where Energy Is Stored]

You are called upon to master and conserve the innate energies of your
mind. This means that you must (1) find out where these energies are
stored, and (2) learn the conditions that determine their activity.

_All past experiences are conserved within us in the form of
complexes. These complexes consist of ideas, emotions and impulses to
muscular activity. By the primary law of association the recall to
consciousness of any one of these component elements of a complex
brings with it all the rest_.

[Sidenote: _Bodily Effects of Ideas_]

For example, the ideas pertaining to any terrifying experience, when
recalled to consciousness, bring with them the trembling, the wildly
beating heart, the shaking knees, with which they were originally
accompanied. The victim of stage-fright feels his knees give way and
that he is sinking to the floor; his heart beats tumultuously, cold
perspiration covers his body, he blushes, his mouth is dry, and his
voice sticks in his throat. Afterwards, alone in his own room, the
memory of that dreadful moment, the thought of another appearance
before that audience, will be accompanied by the same physiological
effects.

[Sidenote: _Impulses and Inhibitions_]

Every such bodily movement is an expression of energy. The recall to
consciousness of the terrifying experience, the recall of the picture
of the assembled audience, these things automatically produce bodily
activities. So we must conclude that _Every idea in memory has
associated with it the potential energy necessary for the produ