ght, and for catching up
any slight arrears which might exist. But the point is that a healthy
body never gets far behind.

If through some flaw in the machine, waste products do pile up, they
destroy the machine. If the heart leaks or the blood-cells fail in
their carrying-power, or if lungs, kidneys or skin are out of repair,
there is sometimes an accumulation of fatigue products which poisons
the whole system and ends in death. But the person with tuberculosis
or heart trouble does not usually allow this to happen. The body
incapacitated by disease limits its activities as closely as possible
within the range of its power to take care of waste matter. Even the
sick body does not carry about its old toxins. The man who had not
eliminated the poisons of a month-old effort would not be a tired man.
He would be a dead man.

=A Sliding Scale.= If all this be true, real fatigue can only be the
result of recent effort. If one is still alive, the results of earlier
effort must long since have disappeared. The tissue-cells retain not
the slightest trace of its effects. Fatigue cannot possibly last,
because it either kills us or cures itself. Up to a certain point, far
beyond our usual high-water mark, the more a person does the more he
can do. As Professor James has pointed out, the rate of repair
increases with the rate of combustion. Under unusual stress, the rate
of the whole machine is increased: the heart-pump speeds up,
respirations deepen and quicken, the blood flows faster, the endless
chain of filling and emptying buckets hurries the interchange of
oxygen and carbon dioxid, until the extreme capacity is reached and
the organism refuses to do more without a period of rest.

The whole arrangement illustrates the wonderful provisions of Nature.
Although each individual is continuously manufacturing enough
carbonic-acid gas to kill himself in a very few minutes, he need not
be alarmed for fear that he may forget to expel his own poisons.
Nobody can hold his breath for more than a few minutes. The naughty
baby sometimes tries, but when he begins to get black in the face, he
takes a breath in spite of himself. The presence of carbonic-acid gas
in the circulation automatically regulates breathing, and the greater
the amount of gas the deeper the breath. The faster we burn the faster
we blow. As with breathing, so with all the rest of elimination and
repair. The body dares not get behind.

="Second Wind."= A city man fr