Proper air and light, proper posture and physical exercise, enough food and sleep, and work whose purpose is rational, whose difficulty is adapted to one's powers, and whose rewards are just, should be tried before recourse to the abandonment of work itself. It is indeed doubtful if sheer rest is the appropriate remedy for a hundredth part of the injuries that result from mental work in our present irrational conduct of it.[2] [Footnote 2: _Ibid_., p. 328.] The study of the conditions of mental work seems to reveal, in brief, that the conditions of fatigue are essentially physical in character. Given adequate physical conditions, in particular guarding against eye-strain, over-excitement (which means distraction from the work in hand), and loss of sleep, mental work is itself peculiarly unaffected by fatigue conditions. The degree in which mental work can be persisted in depends, therefore, other things being equal, on the individual's own interests, the number and intensity of rival interests which persist during a given piece of mental work, and the habits of mind with which the individual approaches his work. The experimental demonstration that so-called mental fatigue is largely physical in its conditions has thus a dual significance. It indicates how arduous and persistent mental endeavor may be and how wide are the possibilities of intellectual accomplishment. It is an important fact for human life that the brain is possibly the most tireless part of the human machine. What seems to be mental fatigue can be materially reduced if the physical conditions under which studying, writing, and all other kinds of mental work are performed are carefully regulated. Another large part of what passes for mental fatigue will be removed if the individual becomes trained to a reflective appreciation of the end of his work. A habit of alert and conscious attention, if it is really habitual, will enable one to persist at work in the face of tempting distractions. Learning to "tend to business" by an intelligent application to the aims of the work to be done, will be a healthy antidote against that yielding to every dissuading impulse which so often passes for mental weariness. CHAPTER V THE SOCIAL NATURE OF MAN