and the brain cannot _functionate_ in their best way at the same
moment. One cannot meditate a poem and drive a saw simultaneously,
without dividing his force. He may poetize fairly, and saw poorly; or
he may saw fairly, and poetize poorly; or he may both saw and poetize
indifferently. Brain-work and stomach-work interfere with each other
if attempted together. The digestion of a dinner calls force to the
stomach, and temporarily slows the brain. The experiment of trying to
digest a hearty supper, and to sleep during the process, has sometimes
cost the careless experimenter his life. The physiological principle
of doing only one thing at a time, if you would do it well, holds as
truly of the growth of the organization as it does of the performance
of any of its special functions. If excessive labor, either mental or
physical, is imposed upon children, male or female, their development
will be in some way checked. If the schoolmaster overworks the brains
of his pupils, he diverts force to the brain that is needed elsewhere.
He spends in the study of geography and arithmetic, of Latin, Greek
and chemistry, in the brain-work of the school room, force that should
have been spent in the manufacture of blood, muscle, and nerve, that
is, in growth. The results are monstrous brains and puny bodies;
abnormally active cerebration, and abnormally weak digestion; flowing
thought and constipated bowels; lofty aspirations and neuralgic
sensations;

"A youth of study an old age of _nerves_."

Nature has reserved the catamenial week for the process of ovulation,
and for the development and perfectation of the reproductive system.
Previously to the age of eighteen or twenty, opportunity must be
periodically allowed for the accomplishment of this task. Both
muscular and brain labor must be remitted enough to yield sufficient