As a matter of fact, by the divine beneficence of Providence, _your organism is so ordered as to adapt itself within certain wide limits to the demands made upon it_. [Sidenote: _Fast Living and Long Living_] You may call into play all the stored-up resources of your being and still not stake everything upon a single throw. For the supply of mental energy is as inexhaustible as the reservoir of all past experience, while the supply of physical energy involved in brain and nerve activity is, like the immortal liver of Prometheus, renewed as fast as depleted. Two sets of facts that have been established by elaborate scientific experiment will convince you of the truth of these propositions. [Sidenote: _Professor Patrick's Experiments_] Professor Patrick, of the State University of Iowa, conducted some of these experiments. He caused three young men to remain awake for four successive days and nights. They were then allowed to go to sleep, the purpose of the experiment being to determine just how much time Nature required to recuperate from the long vigil. They were allowed to sleep themselves out, and all woke up thoroughly rested. _Yet the one who slept the longest slept only one-third longer than his customary night's sleep._ You have doubtless had the same experience yourself many times. It all goes to show that if we are awake four times as long as usual, we do not make up for it by sleeping four times as _long_, but four times as _soundly_, as customary. The hard-working mechanic requires no more hours of sleep than the corner loafer, the active man of affairs no more than the dawdler. [Sidenote: _Ratio Between Repair and Demand_] _The time of tissue repair is about the same with all men under all conditions. It is the rate of repair that varies with the demand that has been put upon the body._ Again, look at the same subject from the standpoint of food supply. On what you now eat and drink you have a certain average weight. Eat, digest and assimilate a larger quantity of food and your weight will increase. This increase will be greatest at the start and will gradually slow up until you shall have reached the point beyond which you can gain no more. Given the same hygienic conditions that you have been accustomed to, you will maintain yourself at the increased weight on the increased supply of food. [Sidenote: _Pygmies and Giants_] Now, all this involves clearly enough a greatly increased rate of activity on the part of the bodily organs of assimilation and repair. It is a situation on all fours with that of the countryman whose rate of brain activity has been stimulated by an increased mental demand. No man will maintain that better, more nourishing and more liberal food rations, transformed into increased bodily tissue, with a consequent greater weight and greater muscular strength, would result in a loss of vitality or the shortening of a man's life. [Sidenote: _Transforming Inertness into Alertness_]