Unconscious cerebration is not, then, a trivial matter, and not an unusual experience. It probably occurs in every individual to a much greater extent than he thinks, unless he is engaged in analyzing his mental processes and their ways rather carefully. This constitutes one of the dangers of the intellectual life, which must also be guarded against in business life or in any absorbing occupation. When the mind has become intensely occupied with a subject, it is not easy to relinquish it. Even when we turn to something else, mental activity in the old groove continues to some extent, and so will prevent the rest that is necessary for the repair of tissue. Under these conditions the re-creation that is so important does not take place quite as well as it should, and even sleep does not relieve us from the burden of mental work. Mental exhaustion will result as a consequence of constant occupation, and so mental relaxation must be secured. Deliberate means and methods must be employed in order that we may not deceive ourselves into thinking we are securing mental recreation, though all the time certain exhausting mental processes continue to be active.

Dual Mental Occupation.—Many are inclined to think that reading, especially the reading of newspapers and magazines, which has become so popular in our time, furnishes an occupation of mind that enables one, for a time at least, to get away from cares and worries. This is probably true when the news is of special interest, or there is some form of excitement, or at the beginning of such reading before one grows accustomed to the usual {139} formula of the magazine stories; but as years go on and cares increase, such reading does not afford an occupation of mind that enables one to throw them off. It helps to pass the time, but the cares and worries keep insistently presenting themselves, and the effort to inhibit them, and at the same time pay some attention to what we are reading, makes a double task. Such reading, then, far from being restful, rather adds to the burden of care and to the labor of the mind, for besides the conscious cerebration, there is the undercurrent of subconscious cerebration disturbing the rest of cells that should be free from labor. The constant renewal of effort to keep one train of thought from interfering with another is itself a waste of nervous energy. This whole matter of reading is coming to occupy a new place in the minds of educators, especially of those who are trying to realize the scientific significance of various phases of education. In his address as the President of the British Association for the Advancement of Science, at the Winnipeg meeting in 1909, Prof. J. J. Thompson, the British physicist, sums up the value of reading as an intellectual exercise in a way that would not be gratifying to those who, in recent years, have apparently accepted the doctrine that in much reading there is much information and, therefore, much education. He says:

It is possible to read books to pass examinations without the higher qualities of the mind being called into play. Indeed, I doubt if there is any process in which the mind is more quiescent than in reading without interest. I might appeal to the widespread habit of reading in bed as a prevention of insomnia as a proof of this.

Social Duties.—So-called social duties are, in this respect, very like reading. When we meet new people who are interesting, we get diversion of mind in their company. When the people with whom we are, however, already familiar, and perhaps most of them a little tiresome, then what is presumed to be a social diversion becomes merely a bore, all the problems of the day obtrude themselves, of real rest there is none, and re-creation can scarcely be possible. Nearly the same thing is true of the present-day theater, after we have become used to its offerings. A serious play, well constructed and with life's problems touched deeply, may grip us and take us out of ourselves, constituting a complete and magnificent diversion. For a limited number of people music accomplishes this purpose. Unfortunately, the number is very limited, and for those for whom music is the greatest diversion, it sometimes constitutes in itself a poignant source of mental exhaustion. Music may be a very trying thing, especially for women, and for those who have souls extremely sensitive to its manifold effects.

Upon these considerations, the importance of unconscious cerebration is brought home to the physician. It is impossible for a great many people to keep their minds inactive, and this is particularly true of two classes of people: those who have superabundant mental energy and those who lack self-control. To both of these classes of men and women, the physician must point out the dangers of unconscious cerebration—the occupation of mind with some subject, even at times while they imagine they are occupied with something else, or even during sleep. Such continuous occupation with a single subject is dangerous. Physicians must emphasize that many supposed {140} mental occupations are really so superficial that they allow other more exhausting processes to continue below them in the sphere of consciousness. As a consequence, the mind, instead of being relaxed, is really more tense than before, because occupied with two sets of thoughts. Very often it would be better for such people to continue with the more serious problem until its solution came, or until they realized that they must divert themselves.