Are you an unusually persevering and persistent person? Or, like most of us, do you sometimes find it difficult to stick to the job until it is done? Suppose that by a determined effort of the will you force your lagging brain to take up the thread of work. There will invariably come a new supply of energy, a "second wind," enabling you to forge ahead with surprising freshness and vigor. The same process may be repeated again and again. Instead of being exhausted by its hours of persistent endeavor the mind can rise to the acme of its power, with difficulties melting into thin air and profound problems finding easy solution. People who work with their heads and people who work with their hands, scholars and Marathon runners alike, can testify to the existence of reserve supplies of power not ordinarily drawn upon.