REST AND ELIMINATION
BODY tissue is continuously undergoing change of structure. The cells that form it are constantly dying, are cast off, and fresh material is supplied. The waste eliminated is poison ; and, without muscular rest, this dead and harmful refuse cannot be replaced with sufficient rapidity by new products. This applies not only to muscles in active use, but to all of the bodily fabric. Rapid exercise of any part of the human machine can be continued but for a short time, for, because of vigorous muscular action, voluntary or involuntary, poisonous substances are thrown into the blood and are carried to tissue, nerves, and brain. Through the nerve cells the heart is affected, and the muscles of respiration are to a similar extent disturbed, and resulting symptoms of self-toxication appear that may end in death. The only means of restoration lies in absolute muscular rest.