should lessen the power of the nerve structures which have only a motor function; but the evidence that it does so is strong. We know, moreover, that the association of various parts of the brain is close. The motor and psychical functions are intimately united; and the action of each may be more necessary for the other than we can yet discern. The strength of a chain is that of its weakest link.

Diminished muscular power is perhaps the least important of the results of brain-fatigue. Those who experience these effects are chiefly brainworkers; and the indications of weariness are more direct. But they are various in their forms, protean to a degree which transcends description. They vary according to the peculiar condition and constitution of the individual; and that which arrests the labor of one person may never be experienced by another. Common to most persons, however, is a sense of diminished brain-power; the "mental grasp" is lessened, and a greater effort is needed for mental work; the memory will not respond readily in voluntary "recollection." Of this, many illustrations are given by Mosso from the experience of his medical friends as to the influence of their lectures and examination work on themselves. Indeed these experiences transcend those of our own countrymen in a degree which suggests that the Italians put more energy into their teaching than we do, and suffer from it far more. One professor who can lecture easily and happily to forty students, finds the task of lecturing to two hundred so severe a strain as to leave him utterly exhausted. The fact is described as independent of the vocal effort to reach the larger number, and as a mere result of the conscious demand of the larger audience. Most Englishmen, we think, would be stimulated by a large number of auditors in a degree

that would facilitate the task, and leave them less tired at the end than they would be after driving the subject, without this stimulus, into a small number. But national temperament is responsible for many differences; and it is important that idiosyncrasies of race should not be assumed to be universal. There is a Yorkshire saying, "Don't measure my corn in your skep," the spirit of which is of wide application.

The extreme variety of the subjective manifestations of mental fatigue experienced by different persons, even of the same race, is forcibly illustrated by a collection of facts made by Mr. Francis Galton. He chose teachers as the persons most likely to give records of the signs of mental fatigue, owing to their double range of observationon their pupils and on themselves. He obtained replies from more than a hundred, and carefully analyzed them. Some evidences of brain-weariness in pupils, which the teachers record, are to be ascribed rather to imperfect attention than to real fatigue. Restlessness is most commonly adduced as a sign of weariness; but the inattention of children, which causes their mobility, is rather to be ascribed to deficiency in the teacher than to fatigue in the pupil as was pointed out by Sir Joshua Fitch in the discussion which followed Mr. Galton's paper. The involuntary muscular actions, which we comprehend under the term "fidgets," are natural to children; but they lessen as years go on, Mr. Galton has himself made some interesting observations on the stillness of learned audiences under a "stiff" lecturer, compared with the constant restlessness of a juvenile audience. Indeed the relation of attention to fatigue is very misleading. The concentration of the mind on a single subject prevents the perception of other sensations. These are felt if the attention is incompletely occupied; they

induce involuntary movements which are mistaken for indications of fatigue. They are no doubt signs of mental weariness, but not of true fatigue. The fact brings out the difference of meaning of the two words and shows that they are not interchangeable. We are often weary when we are not fatigued, and sometimes even because we are not.

The replies given by the teachers to Mr. Galton regarding their own sensations, and the numerous experiences collected by Mosso of the character of personal sensations produced by fatiguing brain-work, show their extreme variety. Their diversities are so great as to make their systematic study extremely difficult; and it is evident that they are largely determined by personal peculiarities. The most definite effect of excessive brain-exertion is imperfect brain-power, analogous to the diminished strength of muscle. But it has features which clearly depend on the characteristics of the individual, unsuspected until thus revealed. The most common feature is failure of memory in its voluntary use, and a weakening of that comprehensive activity in the brain which is described as the "power of grasping a subject." The defect in the volitional memory which is called "recollection" shows itself especially in the use of words, and first, of those that are more special. It often proceeds to a derangement of the secondary symbolism of writing. The writer of a letter produced during thorough brain-fatigue, who is so wise (or unwise) as to read it over, will be surprised to find that he has left out words or miswritten them. He thinks he has misspelt them, and so he literally has; but it is generally an imperfect control of the process of visualizing the letters in words, so that, of two words beginning with the same letter, the first is made to end with the termination which belongs to its successor.

When there is no fatigue, such mistakes are never made. Those who never read through their letters surprise their correspondents; those who do, alarm themselves. The processes for using words as symbols of thought involve many and various forms of brain-activity which are very easily deranged. Thought is symbolized in words, and these are resymbolized in writing; the double process thus af fords evidence of brain-fatigue, at once delicate and obtrusive.

When we pass to other manifestations of fatigue, we find that they largely depend on personal weakness, and we meet with many varieties which are of no general significance; they are, indeed, only important in their negative character, and their peculiarities are purely due to idiosyncrasy. For example, among the facts collected by Galton as signs of fatigue is a tendency for the letters of print to run together when the reader is tired. This is simply due to overwork in the muscle within the eye which adjusts the focus. The muscle is inherently weak in that particular individual, and it fails before other parts in consequence of general nervous fatigue; but the failure has no other significance. Other personal effects of fatigue which he mentions, such as transient color-blindness, are susceptible of the same explanation.

By far the most common effects of over-use of the brain are sensory in nature, definite "feelings." They are almost appalling in their variety and degree. The distress they cause suggests the thought that the human brain has been compelled to work too soon, before the lower functions of the nervous system have been developed enough to counterbalance the employment of the higher, so that the weight of mind is more than can be borne. The most common of these sensory effects of fatigue is headache. Common

as it is, there are many persons to whom it is unknown; and its actual origin is still a mystery. The brain can be handled and cut without pain, and yet is, in some way, the source of severe suffering in mere functional disturbance. But other parts of the body present the same strange feature. The intestines normally give rise to no sensation, and yet undue contraction causes intense agony. A healthy person is not aware that he has a delicate membrane covering the lung, called the "pleura," which is stretched when the lung expands in breathing without the least sensation being produced. But if this membrane is inflamed in what is called "pleurisy." acute pain is produced each time the breath is drawnan experience which has been endured by the majority of persons of middle age. The occurrence of headache, of pain in a brain that seems insensitive, is thus not a unique event, and yet it is hard to understand. It is often replaced by other sensations almost as distressing. But one character of these sensations, which is a matter of common experience, is very curious; it is the sensation of "thickness" or "cloudiness" or "denseness" of the brain which results from overwork. It is a purely physical sensation, which seems to be in the brain itself, and yet it corresponds every closely to the condition of the mental processes.

These cerebral sensations which fatigue produces are almost inexplicable, but they naturally turn our thoughts to those that are felt in the muscles after much exertion, to which they bear some resemblance. We have seen that these may be ascribed to products of muscular work acting on the sensory nerves. It is reasonable to think that the brain sensations are produced by an analogous mechanism. The action of the cerebral structures must result in the formation of lower chemical compounds analogous to those

which are produced in muscle. The nerve tissue is more sensitive, and must be more readily influenced. But our present difficulty is that we do not know where the perceptive element exists in the brain tissue. A few years. ago, however, we did not know where the sensory element existed in the muscle; and we may hope that the mystery which has there been solved will also be made clear in the brain. In all sciences the first essential element is the discernment of facts. When these are clearly seen, our work must be guided by them; or our efforts are futile. The old saying that "facts are stubborn things" is always true. When their existence and form are discerned, all theory must adapt itself to them and explain them, or be dismissed, in Ruskin's phrase, as "thistle-down without seed."

Precise observation is however much baffled by varieties in the sensory susceptibility of individuals. It is probable that these depend on differences in the actual constitution of the nervous tissue-more minute than we can well conceive, and yet causing effects that are obtrusive. In different persons there may exist diversities of tissue which give rise to great differences in the products of action, rendering these much more harmful in one person than in another. The same diversity may render the sensory structures far more prone to disturbance, and to more distressing disturbance. Thus an original variation which, if it could be discerned, would be minute almost beyond conception, may entail a profound difference in ultimate effect. Such considerations may help us to conceive the way in which the effects of fatigue are manifested, although they constitute little addition to our knowledge.

Another class of fatigue effects can only be understood on the same hypothesis of peculiar constitution. Instances of disturbed function in the organs of

the body figure frequently among the facts that Galton has gathered from the personal experience of teachers, and that Mosso has recorded as the results of lecturing and examining, felt by himself and his colleagues. Mosso has investigated them with precision; but he has ascertained little more than the fare facts. The action of the heart, the functions of the stomach, and the work of the liver and other organs, are disturbed in various ways; and even the temperature of the whole body is sometimes altered by hard memtal work. But such derangements of organs produce their own independent effect; they act especially on the blood, and thus prolong the discomforts due directly to fatigue. One great function of the liver is to eliminate the harmful products of muscular action; and whatever interferes with this process augments the amount of toxic substance in the blood.

It may be reasonably asked, What is the relative importance of the signs of brain-fatigue? We cannot doubt that any indication of failure of brainpower transcends all others in absolute importance. The physical sensations that occur are of slight and merely personal significance compared with defects of memory, of concentration of thought, or of the use of the muscles for such processes as writing. But, to the individual, the varied sensory disturbances which are produced by overwork are equally important, because they are equally distressing. They tend to grow by the fostering effect of repeated production; and those which are of no intrinsic significance may, by the distress they cause, be utterly disabling.

Another question often asked is, What amount of truth is there in the familiar doctrine that fatigue is prevented by change of work? If only the work is not too heavy, we can discern the reasonableness of this belief. Any

special form of mental occupation involves the use of the nerve structures in a definite degree and a particular combination. Even the nerve elements in the same region of the brain may be active or not, intensely energetic or slightly active, according to the precise character of the cerebral process. All functional action stimulates nutrition, and is definitely beneficial, provided it does not exceed a moderate degree. Indeed, absolute rest is apparently unknown to the elements of the nervous system. They are in constant, gentle, unperceived activity. In all parts of the body, on the surface and in the internal organs, impressions are constantly arising, for the most part unperceived, which cause activity of the afferent nerves and of their related central structures, processes which spread widely, even to the motor structures and the motor nerves, and maintain the muscles in their state of firmness or tone, itself essential for the muscular nutrition. This constant activity entails nutritional changes in the elements, necessary for the maintenance of their normal state. Their constituent atoms are always passing away, and always being renewed; were it not so, it would be impossible for them to pass into the state of energetic action that may be evoked at any moment. These changes seem to be the nutritional counterpart of the gentle action we can discern; and both are essential for the life of the structures. Their increase within moderate degree by work involves increased nutritional change, a greater vital efficiency. A different form of mental work may thus involve the gentle activity that is conducive to better replacement of old constituents by new, and may thus promote the general wellbeing of the brain.

Moreover we can discern another reason for the beneficial influence of the change of work. By a wonderful

mechanism, which we imperfectly comprehend, all functional activity is attended by an increased blood-supply. The minute vessels which convey the blood dilate; and more blood passes to the acting tissue than to one that is quiescent. Hence there is a more abundant supply of the nutritive plasma, which passes from the vessels to the tissues laden with fresh material from which the nerve elements appropriate what they need. But the arrangement of the vessels which convey the blood bears only a very general relation to the functions of the brain. In the same part different layers of the brain may have different functional relations; they may be involved in very different degrees in various forms of brain activity; yet the dilatation of the vessels and the increased blood-supply involve them all alike. The increased flow of the blood, and increased access of the elements essential to replace those which are lost in action, involve an augmented supply to all the tissues in that region, to those which have been only slightly called upon as well as to those which are more or less exhausted. On the other hand, the work of the tissue means an escape of its used-up elements, and a need for their removal, as well as for the fresh supply which the increased flow of blood affords. Thus we can understand that the old belief has a distinct and intelligible foundation. A different form of activity may leave the exhausted elements almost at rest, and yet aid the renewal of their lost material and promote the removal of the waste products.

The same considerations apply to muscular exercise in even greater degree. Although the region of the brain The Quarterly Review.

chiefly employed may not be the same, all parts share such activity; and for all parts the blood supply is augmented, not only as a result of functional activity, but as the effect of the stimulation of the whole circulatory system which physical exercise involves. The heart beats faster; and the respirations, being quickened, augment the supply of oxygen which the muscles demand but which goes also to the whole system. The purer the air inspired, the greater is its beneficial influence; and hence the advantage of exercise in the open air. But, to be useful, exertion must be moderate. In excess, as we have seen, the brain is hindered by the products of its own action, as well as by those of the muscles; for all physical effort involves corresponding activity of the motor centres in the brain.

We are accustomed to talk of "recreation" without discerning how much the word implies. It means "making again" that which work has undone, or rather facilitating the marvellous recuperative power of life. Rest and recreation are the antidotes of fatigue; but recreation should be such as to deserve the name. It does not replace rest, but, properly employed, aids its influence. Its value is great in propor tion as it involves a thorough change in the character of nerve activity. But it should always be remembered that no recreation is possible if that which is thus designated simply replaces one form of fatigue by another form. Many a holiday is rendered useless by such disregard of the dictates of that rare practical wisdom to which, as if in irony, we apply the designation "common-sense."

W. R. Gowers.