When a man uses his muscles, after a time comes the feeling called fatigue--a sensation always referred to the muscles, and due most probably to the deposit in the tissues of certain substances formed during motor activity. Warned by this weariness, the man takes rest--may indeed be forced to do so; but, unless I am mistaken, he who is intensely using the brain does not feel in the common use of it any sensation referable to the organ itself which warns him that he has taxed it enough. It is apt, like a well-bred creature, to get into a sort of exalted state under the stimulus of need, so that its owner feels amazed at the ease of its processes and at the sense of wide-awakefulness and power that accompanies them. It is only after very long misuse that the brain begins to have means of saying, "I have done enough;" and at this stage the warning comes too often in the shape of some one of the many symptoms which indicate that the organ is already talking with the tongue of disease.
I do not know how these views will be generally received, but I am sure that the personal experience of many scholars will decide them to be correct; and they serve to make clear why it is that men may not know they are abusing the organ of thought until it is already suffering deeply, and also wherefore the mind may not be as ruthlessly overworked as the legs or arms.
Whenever I have closely questioned patients or men of studious habits as to this matter, I have found that most of them, when in health, recognized no such thing as fatigue in mental action, or else I learned that what they took for this was merely that physical sense of being tired, which arises from prolonged writing or constrained positions. The more, I fancy, any healthy student reflects on this matter the more clearly will he recognize this fact, that very often when his brain is at its clearest, he pauses only because his back is weary, his eyes aching, or his fingers tired.
This most important question, as to how a man shall know when he has sufficiently tasked his brain, demands a longer answer than I can give it here; and, unfortunately, there is no popular book since Ray's clever and useful "Mental Hygiene," and Feuchtersleben's "Dietetics of the Soul," both out of print, which deals in a readable fashion with this or kindred topics.[[3]] Many men are warned by some sense of want of clearness or ease in their intellectual processes. Others are checked by a feeling of surfeit or disgust, which they obey or not as they are wise or unwise. Here, for example, is in substance the evidence of a very attentive student of his own mental mechanism, whom we have to thank for many charming products of his brain. Like most scholars, he can scarcely say that he ever has a sense of "brain-tire," because cold hands and feet and a certain restlessness of the muscular system drive him to take exercise. Especially when working at night, he gets after a time a sense of disgust at the work he is doing. "But sometimes," he adds, "my brain gets going, and is to be stopped by none of the common plans of counting, repeating French verbs, or the like." A well-known poet describes to me the curious condition of excitement into which his brain is cast by the act of composing verse, and thinks that the happy accomplishment of his task is followed by a feeling of relief, which shows that there has been high tension.
One of our ablest medical scholars reports himself to me as having never been aware of any sensation in the head, by which he could tell that he had worked enough, up to a late period of his college career, when, having overtaxed his brain, he was restricted by his advisers to two or three hours of daily study. He thus learned to study hard, and ever since has been accustomed to execute all mental tasks at high pressure under intense strain and among the cares of a great practice. All his mind-work is, however, forced labor, and it always results in a distinct sense of cerebral fatigue,--a feeling of pressure, which is eased by clasping his hands over his head; and also there is desire to lie down and rest.
"I am not aware," writes a physician of distinction, "that, until a few years ago, I ever felt any sense of fatigue from brain-work which I could refer to the organ employed. The longer I worked the clearer and easier my mental processes seemed to be, until, during a time of great sorrow and anxiety, I pushed my thinking organs rather too hard. As a result, I began to have headache after every period of intellectual exertion. Then I lost power to sleep. Although I have partially recovered, I am now always warned when I have done enough, by lessening ease in my work, and by a sense of fulness and tension in the head." The indications of brain-tire, therefore, differ in different people, and are more and more apt to be referred to the thinking organ as it departs more and more from a condition of health. Surely a fuller record of the conditions under which men of note are using their mental machinery would be everyway worthy of attention.
Another reason why too prolonged use of the brain is so mischievous is seen in a peculiarity, which is of itself a proof of the auto-activity of the vital acts of the various organs concerned in intellection. We sternly concentrate attention on our task, whatever it be; we do this too long, or under circumstances which make labor difficult, such as during digestion or when weighted by anxiety. At last we stop and propose to find rest in bed. Not so, says the ill-used brain, now morbidly wide awake; and whether we will or not, the mind keeps turning over and over the work of the day, the business or legal problem, or mumbling, so to speak, some wearisome question in a fashion made useless by the denial of full attention. Or else the imagination soars away with the unrestful energy of a demon, conjuring up an endless procession of broken images and disconnected thoughts, so that sleep is utterly banished.
I have chosen here as examples men whose brains are engaged constantly in the higher forms of mental labor; but the difficulty of arresting at will the overtasked brain belongs more or less to every man who overuses this organ, and is the well-known initial symptom of numerous morbid states. I have instanced scholars and men of science chiefly, because they, more than others, are apt to study the conditions under which their thinking organs prosper or falter in their work, and because from them have we had the clearest accounts of this embarrassing condition of automatic activity of the cerebral organs. Few thinkers have failed, I fancy, to suffer in this way at some time, and with many the annoyance is only too common. I do not think the subject has received the attention it deserves, even from such thorough believers in unconscious cerebration as Maudsley. As this state of brain is fatal to sleep, and therefore to needful repose of brain, every sufferer has a remedy which he finds more or less available. This usually consists in some form of effort to throw the thoughts off the track upon which they are moving. Almost every literary biography has some instance of this difficulty, and some hint as to the sufferer's method of freeing his brain from the despotism of a ruling idea or a chain of thought.
Many years ago I heard Mr. Thackeray say that he was sometimes haunted, when his work was over, by the creatures he himself had summoned into being, and that it was a good corrective to turn over the pages of a dictionary. Sir Walter Scott is said to have been troubled in a similar way. A great lawyer, whom I questioned lately as to this matter, told me that his cure was a chapter or two of a novel, with a cold bath before going to bed; for, said he, quaintly, "You never take out of a cold bath the thoughts you take into it." It would be easy to multiply such examples.
Looking broadly at the question of the influence of excessive and prolonged use of the brain upon the health of the nervous system, we learn, first, that cases of cerebral exhaustion in people who live wisely are rare. Eat regularly and exercise freely, and there is scarce a limit to the work you may get out of the thinking organs. But if into the life of a man whose powers are fully taxed we bring the elements of great anxiety or worry, or excessive haste, the whole machinery begins at once to work, as it were, with a dangerous amount of friction. Add to this such constant fatigue of body as some forms of business bring about, and you have all the means needed to ruin the man's power of useful labor.