for a definite purpose, imposes so great a physiological task, will
not have as much power left for the tasks of the school, as the boy of
whom Nature requires less at the corresponding epoch. A margin must
be allowed for growth. The repair must be greater and better than the
waste.

During middle age, life's active period, there is an equilibrium
between the body's waste and repair: one equals the other. The
machine, when properly managed, then holds its own. A French
physiologist fixes the close of this period for the ideal man of the
future at eighty, when, he says, old age begins. Few have such
inherited power, and live with such physiological wisdom, as to keep
their machine in good repair,--in good working-order,--to that late
period. From the age of twenty-five or thirty, however, to that of
sixty or sixty-five, this equilibrium occurs. Repair then equals
waste; reconstruction equals destruction. The female organization,
like the male, is now developed: its tissues are consolidated; its
functions are established. With decent care, it can perform an immense
amount of physical and mental labor. It is now capable of its best
work. But, in order to do its best, it must obey the law of
periodicity; just as the male organization, to do its best, must obey
the law of sustained effort.

When old age begins, whether, normally, at seventy or eighty, or,
prematurely, at fifty or thirty, repair does not equal waste, and
degeneration of tissue results. More cells are destroyed by wear and
tear than are made up from nutriment. The friction of the machine rubs
the stuff of life away faster than it can be replaced. The muscles
stiffen, the hair turns white, the joints crack, the arteries ossify,
the nerve-centres harden or soften: all sorts of degeneration creep on