. Then you should _exercise_ the specific brain
center and set of muscles in the production of mental reflexes, or the
mind fruit. Acts of courage, for example, are the fruit of brave
thoughts.

[Sidenote: Brain Development]

A particular brain center, of course, will be strengthened both by the
_food_ of sense impressions it is given, and by the _exercise_ of
handling messages to and from the mind. The brain, or physical
instrument of the mind, is like an intermediary or go-between of the ego
and the body. It is of the utmost importance that it should do its work
efficiently. Otherwise the full capability of neither the outer nor the
inner man can be utilized.

If Brown passes something to Jones, who passes it along to Smith; then
Smith passes it back to Jones to be re-passed to Brown--Jones, the
middle agent of transmission or handling instrument, whom we are
comparing to the brain, might be so awkward, slow, and inefficient as a
go-between that the possible ability of Brown and Smith in passing would
be nullified or greatly hampered. But if the inefficiency of Jones is
blamable to his inexperience, it evidently can be changed to efficiency
by _sufficient right exercise_ in passing. The more of that sort of work
he does, in either direction, the better passer will Jones become.

His exercise, however, must be _in passing_ things, if _passing_
capability is to be developed. He would not become a better and quicker
_passer_ by any amount of exercise in taking things apart, or in
inspecting things--wholly dissimilar functions.

[Sidenote: Training in Passing]

Moreover, Jones would not become an expert passer of _glassware_ as a
result of practice in passing _bricks_, for the two kinds of things are
not handled alike. Indeed, the man accustomed to passing bricks might be
more likely to break glassware than another man who previously had no
particular skill in passing anything. The expert brick-passer would be
apt to forget sometimes that he was passing glass. His muscles might
treat the fragile ware with the rough habit acquired in passing bricks.

Plainly, discriminative-restrictive methods of training are required to
perfect capability in any _particular_ kind of physical passing; however
much skill in _general_ passing may have been developed. If Jones should
become expert in passing pails of liquid, he would nevertheless need to
train himself anew in order to pass frozen liquid efficiently in the
form of cake