Over-exertion may produce exhaustion, which, in a person before feeble, may end in death. Or, short of this, there may be brought on a state of weakness slow to be recovered from. In such a state, moreover, 468 the body is less capable of resisting all causes of disease than when in full vigor.

Excessive efforts may, at the time, strain muscles, or even burst the heart, or the great main artery, the aorta.

Over-excitement of the brain is, in many cases, when it lasts but for a short time, followed simply by exhaustion and gradual return, through repose, to ordinary health. But long-continued excessive mental excitement may produce either inflammation of the brain, insanity, or prolonged brain-exhaustion . Loss of sleep, however induced, endangers such effects. Hardly any one can survive deprivation of sleep for so long as two weeks at a time ; a single week would finish most peoples' lives.