CHAPTER I.

POWER OF RESISTING FATIGUE.

Variability in the Power of Resisting Fatigue-Effects of Inaction-Effects of Habitual Activity-Different Mode of Life causes Different Conformation; Frugivorous Animals and Hunting Animals; the Flesh of the Hale and the Flesh of the Wolf-The Labourer and the Scholar-How we must explain "Habituation" to Work.

MEN who have for a long time abstained from bodily exercise, and whose system most keenly suffers from the want of it, are those by whom fatigue is most to be dreaded, and those who have most risk of suffering from overwork. Those who, on the contrary, daily perform muscular work acquire the power of braving fatigue and successfully striving against its most serious manifestations.

But this immunity which is gained by work is very quickly lost by inaction; it can only be preserved by the habitual practice of muscular exercise.

We may say that too prolonged repose is the condition which most effectively predisposes the organism to fatigue. Stiffness is unknown to men who lead a life of continual muscular activity, and the consequences of overwork affect them with difficulty. Fatigue in all its forms and all its degrees especially makes its effects felt on those who take too much rest. We see women who never walk a step in the street; their carriage renders it unnecessary; they do not even make any movements in dressing themselves; they have a maid to save them the trouble. These persons suffer from stiffness if they walk the length of the street. If one day by chance, on the advice of their medical man,

they decide upon an hour's walk, they are in bed with a fever the next morning. The doctor is sent for with all speed, and it is explained to him how barbarous he has been to compel his patient to use her legs. On the other hand, a postman in the country walks his 20 to 25 miles a day, goes to bed without feeling any the worse, and wakes up each morning the more fit for his walk.

Moral energy is not the true source of the power of resisting fatigue. In most cases what makes the difference between the power for work of two persons is less the manner in which they are physically and morally endowed than the preparation they have undergone or the life they have led; it is less a matter of temperament than of acquired aptitude.

Amongst domestic animals there are great differences in the matter of fitness for work. Wild animals, on the contrary, have sensibly the same power of enduring prolonged muscular effort. Two wolves of the same age have nearly the same speed and the same staying power. Two dogs, even from the same litter, often show considerable differences in their power of resisting fatigue. The differences which domestic animals present among themselves as regards the power of resisting fatigue is due to the numerous variations in their mode of life to which domestication leads. The remarkable equality of wild animals, from the same point of view, is due to the similarity of their conditions of existence.

What are the conditions producing power of resisting fatigue ? This question was long ago answered empirically, and by facts. We know that the practice of certain muscular exercises associated with certain rules of diet, called as a whole training, very quickly induces in men and other animals the power of supporting, without ill effect, a violent and prolonged exercise which, without such preparation, would have had serious consequences to the system. We also know that, the power of resistance due to training is lost as soon as the animal returns to the mode of life which he had for a time given up.

Why does a man who daily performs muscular exer

cise acquire, by the very fact of working, the power of working without fatigue? A very simple answer is usually given to this question: it is said that the man has become accustomed to fatigue. Those who wish to give their explanation a more scientific ring speak of the "habituation" of the body to work.

If we consider fatigue as pain, it is absurd to say that a man becomes accustomed to fatigue. A man cannot become accustomed to pain so as not to feel it any longer. Ask a man suffering from severe neuralgia if he suffers less because he has been suffering for a long time! It is not right to say that a man accustomed to work "supports" fatigue well. He has not to support it at all, for it is not produced.

A well-trained man resists fatigue easily, not because he despises the painful sensation which habitually accompanies work, in the way in which the Stoics despised pain, but because this sensation is not produced in him, or at least is produced in a very slight and easily bearable degree. Thus the power of resisting fatigue is not due to the greater tolerance of the worker, but to the diminished intensity of the discomfort to be borne.

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The power of resisting fatigue is due to a material change produced by an exercise which is often practised in the structure of the organs by which the work is performed. When we say that a man is "hardened fatigue, this expression must be taken in its literal, never in its figurative sense. Work produces in all the tissues of the body changes of nutrition which make them more resistant, firmer, which in a sense arms them against shocks and friction, and insures them against the accidents of work. Prolonged repose, on the other hand, makes the tissues softer and more vulnerable.

A gardener who works from morning till night does not hurt his hands by holding the spade; a scholar who performed the same exercise for an hour would complain that his hands were painful. Has the gardener, then, more energy than the savant? No; he merely has a thicker skin. No blisters form on the callous skin which covers the parts of his hands habitually in contact with

the tool. This is as evident as it is possible. It gives us an example of what occurs daily in the organism under the influence of work. Every organ which works undergoes a material change, from which results a greater fitness for performing work without being pained by it.

Through daily exercise the muscles become harder and more elastic: they are thus more ready to resist shocks and strains, more fitted also to protect from external violence the sensitive parts which they cover: nerve filaments and internal organs. A well-trained boxer no longer feels a blow with the fist, his flesh has become so hard that it is not injured by the blow; it is the fist of his adversary which is injured by striking it.

Exercise does not merely harden the skin and the muscles; it consolidates all the organs of work. Domestic animals which do hard work acquire tough and solid tendons. Amongst wild beasts there is a great difference between frugivorous and carnivorous. animals. The flesh feeders which live by the chase and are always on foot to watch for and pursue their prey, show to an extreme degree the type of the trained animal. Their tendons, the fascia which sheathe their muscles, and the muscles themselves, are as hard as wood. To get an idea of the hardness of the tissues in a hunting animal, it is necessary to dissect, as we have done, an old wolf. The knife will hardly cut the tendons and fibrous tissue. Similarly with birds which live by the chase, the falcon and the hawk. All the animals which lead a life of rapine and brigandage are in continual movement, and the uninterrupted exercise changes the structure of their organs so as to give them a surprising power of resistance.

The other wild animals which live on plants have a quite different organization. The hare, the partridge the quail, saving the flights given them from time to time by the hunter, pass their time in feeding on a nutriment which abounds at every turn; they sleep peacefully and do very little. And their flesh is fat and tender, their muscles soft and saturated with savoury juices. We eat the hare and the quail, their flesh melts

in our mouth; we do not eat the flesh of the falcon or the wolf; we should leave our teeth in it.

It is the difference of work which causes the marked differences of structure observed in animals. The same differences are to be seen in man. If we dissect a man who throughout life has performed violent exercises or hard work, we are struck by the remarkable power of resistance and by the solidity of all the tissues concerned in movement. We easily understand how these large and firm muscles, these thick and solid fascia, these tendons, dry and hard as steel, could resist without suffering all the shocks of work.

The bones themselves become adapted, by an increase in size and density, to the more energetic work of the muscles attached to them. The bones of horses which have done violent work in a circus for some years have been weighed, and compared with those of horses of the same build which have spent their life quietly at grass; the skeletons of the circus horses were much heavier, their bones were harder and firmer. In man also, muscular work causes an appreciable change in the nutrition of the bones. It is easy to say, by simple examination of a human skeleton, whether the person to whom it belonged has led a life of muscular activity, or if he has lived in physical idleness. The bony points to which the muscular fibres are attached are smooth and regular if the muscles have been inactive: on the contrary if the man was active, the points of muscular attachment are prominent, and there are roughnesses which furnish. a stronger attachment to the fibres.

Besides these changes which are so easily discovered in the organism as a result of work, there are certainly many others of which we know less. There is no absurdity in thinking, for instance, that the epithelium of the synovial membranes must undergo, under the influence of the energetic friction caused by work, changes analogous to those occurring in the thickened epidermis, and thus become more able to support severe pressure without injury. Similarly, everything leads us to believe that the nerve filaments which pass through the muscles