sensation of fatigue has its seat rather in the nervecentres than in the muscles. Whenever muscular work is performed without the brain taking part in it, we notice that fatigue is much more slowly produced; while it is more intensely manifested the more vigorously the cerebral faculties are associated in the performance of the action.

Many movements are involuntary and unconscious; the movements of organic life, the heart-beat, the respiratory movements. None of these movements, which are performed without the intervention of the brain, and independently of the will, ever determine the sensation of fatigue.

At each contraction the heart exercises a force capable of raising through a height of one centimetre a weight of forty kilogrammes, and it contracts sixty times per minute. Which of our limbs could carry on such a labour for a quarter of an hour? We may say the same of the muscles which bring about the respiratory movements. They contract sixteen times per minute and never rest; they work incessantly from birth till death, and never become fatigued.

The muscles ordinarily under the control of the will have the same immunity from fatigue when their contraction is involuntary. In hysterical contracture, in catalepsy, in hypnotism, the patient, whose will is not in action, easily supports the most fatiguing positions without being fatigued. In chorea, or St. Vitus' dance, we see the patients making violent movements without intermission from morning till night. A man who endeavoured to perform the same movements voluntarily would have to stop to rest in a very short time. But these patients do not complain of the sensation of fatigue.

Thus the same muscular work which produces fatigue, when it is voluntary, no longer produces it when it is done without the intervention of the will, that is, when the brain does not associate in the performance of the muscular action.

The brain then, is most probably the seat of that

sensation which causes cessation of work before the muscles are really fatigued. In voluntary movements, the more intimate the association of the brain with the muscular action, the more intense the sensation of fatigue. An exercise which is accompanied by a considerable tension of the will is more fatiguing than one performed independently of the will. Sometimes work which needs an insignificant expenditure of force, causes very prompt lassitude when it is executed with a sustained attention, that is to say when the will is not relaxed for an instant.

A man taking riding-lessons becomes much more tired in the narrow limits of the riding-school than he would by riding a long distance at a trot. In the first case the will must preside with a vigilant care over all the actions of the horseman's legs, and over the reins. In the second case, the body, accustomed to the horse's paces, automatically accommodates itself to the movements of trotting, and the brain takes no part in the exercise.

Few things vary as much as the susceptibility of different persons to fatigue. Very nervous and very irritable individuals feel sometimes too keenly the painful sensations which accompany muscular work, and they are then placed in this dilemma: whether to stop when fatigue is first felt, and do less exercise than they really require, or to resist fatigue and expose themselves to the nervous reaction which follows, in such persons, any considerable pain. Nervous hyperexcitability often results from the struggle of an enfeebled man against the discomfort which work causes him, and compels the doctor to forbid exercise to such a patient, to whom it would be most valuable if it could be endured.

In these cases we can always manage to make exercise supportable, but it is necessary carefully to consider the form under which it will have the best chance of being borne, that is to say the form which will cause least fatigue.

We can here only indicate broadly how to proceed in

such cases, in which medication by exercise needs much tact, and a profound study of each exercise performed. Here we shall only formulate this law:

The muscular work being equal, the sensation of fatigue is the more intense, the more active the intervention of the cerebral faculties demanded by the

exercise.

Consequently, in dealing with very nervous persons, it will be necessary to employ exercises which do not need a sustained attention, those of which the movements are easy, and as much as possible, automatic; walking, for instance.

CHAPTER II.

BREATHLESSNESS.

A Hard Run-Exercises which cause Loss of Breath; Trotting and Galloping; Going Upstairs--Law of BreathlessnessRespiratory Need; Conditions under which it Increases and Diminishes-Carbonic Acid; its Production Increases with Muscular Activity; it Diminishes during Repose-The Sleep of the Marmot-Explanation of the Law of BreathlessnessWhy we lose Breath in Running-Why the Horse Gallops with its Lungs-Why Exercises of the Legs cause more Loss of Breath than those of the Arms-The Coefficient of Breathlessness-The Horse which exceeds its Paces-Breathlessness is an Auto-Intoxication by Carbonic Acid-Analogy with Asphyxia--Impossibility of Fighting against Breathlessness.

HAVE you ever found yourself within sight of the station and been afraid of missing the train? You have a quarter of a mile to traverse, and you see from your watch that you have only two minutes. You will have to run, and for years you have been accustomed to the measured pace of the man who walks when he has plenty of time and takes a cab when he has not. But you want to catch that train, and plucking up courage you set off as hard as you can run.

Your legs are strong and it does not hurt them when you run. However, after a few seconds, a peculiar distress seizes you. Your breathing is embarrassed, a weight seems to press you down, and a bar to be fixed on your chest. Your respiratory movements become jerky and irregular. With each step distress increases and becomes more general. Your temples throb violently, an insupportable heat rises to your brain, an iron band is tied round your forehead. Then there is a singing in your ears, your sight is disturbed, and you

have but a confused idea of the objects you pass, and of the people who turn to stare at your pale and dishevelled figure.

You reach your goal. As the train whistles you sink exhausted on the cushions of your compartment. There, in spite of the satisfaction of having caught your train, and the solace of being seated, your distress continues. Still for some minutes you are out of breath, and the hurried movements of your chest make you resemble a man seized with a violent attack of asthma. This is what we call "being winded."

We are seldom astonished by things which we see every day, and it seems natural to every one that a man should be out of breath when he has been running. But if we think about the matter, there is something surprising in the phenomenon of breathlessness while running when we run the legs do the work and the lungs become fatigued.

I.

No methodical exposition and rational explanation of breathlessness have hitherto been given. This form of fatigue has not as yet been the subject of any monograph; it is not described in any great dictionary of medicine nor in any physiological text-book.

There is however, no phenomenon more common and more frequently observed than breathlessness; there is none more interesting from the point of view of the hygienic and therapeutical results of muscular exercise.

Breathlessness is a feeling of distress which is produced during violent exercise or intense muscular work, and it is characterised by an exaggeration of the respiratory need, and by profound disturbance in the functions of the respiratory organs. This state is merely a peculiar form of dyspnoea and presents the general phenomena due to deficient aeration of the blood. But it differs from the respiratory troubles which we notice in morbid conditions by certain special signs which we shall point out, and above all in the conditions in which it is produced and in the mechanism of its production.