effort! The muscular work has not increased, for the weight is always the same, but the nervous work is doubled because the fatigued muscle has become less irritable and must, if it is to contract, be more strongly stimulated by the nerve. Hence the necessity that the will should produce a more violent vibration in the nerve-centres, a more intense disturbance, the effects of which are translated, when the work is over, by a kind of enfeeblement, of temporary prostration, which always follows great expenditure of nerve-force, equally in the psychical and the physical order.

It is easy, with the aid of electricity, to imitate experimentally all the phenomena of muscular contraction, and to render evident the disproportion produced by fatigue between the quantity of force expended by the fatigued muscle and the intensity of the stimulus which it receives. If we stimulate a muscle by means of a current of graduated intensity and fit to one of the extremities of this muscle a dynamometer indicating the force with which it contracts, we observe that after a series of contractions the muscle becomes weaker although the intensity of the current has not diminished. In proportion as the work is prolonged the response of the muscle to each stimulus becomes more and more feeble, and finally ceases altogether. If we now gradually increase the intensity of the current we see the contractility of the fibre gradually reappear, and the dynamometer indicate a stronger and stronger contraction which at last becomes as strong as it was at first. But the current is now stronger, and a contraction of the energy of that which was at first produced by a current represented by the figure I may now need for its production a current represented by the figure 2.

The necessity of drawing from a muscle all the vigour it possesses is not the only circumstance of physical exercise which needs supplementary nervous work. We shall see in the following chapters under how many different forms work of the brain is added to work of the muscles in the course of exercises of the Body.

CHAPTER IV.

WORK OF LATENT STIMULATION.

A Cat lying-in-wait for a Mouse-Lying-in-wait in Animals. Nervous Work which this Action needs-Identity of Certain Phases of Bodily Exercise with the Phenomenon of lying-inwait A Fencing Bout-Physiological analysis of the "Direct Blow"-Fencers who have "Quickness "-Readiness of BlowLatent Stimulation of Muscle and Diminution of the Latent Period-Explanation deduced from the Discovery of Helmholtz -The Office of the Brain in Fencing-How the Fencer betrays his Intentions-Advice of Bazancourt. Effects of Work of Latent Stimulation-Nervous Fatigue and Intellectual Fatigue-Nervous Fatigue; its Effects on Nutrition-Why Cats do not become Fat. HAVE you ever watched a sleeping cat suddenly awakened by the nibbling of a mouse? It starts up and pricks up its ears. Look at it lying in wait: not a muscle moves. In its absolute immobility it seems still to sleep; but its bristling whiskers and sparkling eyes announce that a more intense life animates its outwardly inert body; all its limbs are stretched like springs, and its muscles, under the influence of powerful nervous stimulation, only need a last push to throw them into violent action.

When the mouse appears its capture is instantaneous: with the rapidity of lightning the animal has sprung and given a deadly blow with its claws.

To obtain this sudden transition from immobility to action, the cat had prepared its muscles, distributing to each a supply of nervous energy, keeping them as it were awake in an intermediate state between repose and action. In physiology we give the name of latent stimulation to this preparation which the muscle must undergo to become more fitted for instantaneous obedience to the orders of the will.

Latent stimulation of the muscles is an expenditure of force which eludes all mechanical estimation, for it is not outwardly translated by work in kilogrammetres ; but it is a physiological action which does not pass unnoticed by the nervous system, and which must be taken into consideration in the analysis of a bodily exercise. When a cat lies in wait for a mouse, the fatigue of the chase does not consist in the bound which the animal makes to seize its prey, but in the nervous tension which precedes this movement.

We have an opportunity of studying, in numerous hunting animals besides the cat, this very interesting action of lying-in-wait. In hunting dogs training and inheritance have caused the disappearance of the second part of this act, which is its natural termination. A thoroughbred pointer never gets beyond the stage of lying in wait, and never bounds upon its prey, but its muscles do not escape that latent stimulation, which, in principle, has the object of rendering them more ready for action, and which, in shooting dogs, has been developed into a peculiar attitude indicating to the sportsman the presence of game.

Many exercises, and these common ones, need a preliminary preparation of the movements which recalls in a surprising manner the phenomena of "lying in wait"; these are exercises in which quickness assumes the character of suddenness. Whenever the muscles must pass instantaneously from immobility to action, and that at the precise moment when there is the best opportunity for the movement, a very intense nervous work must precede the muscular action; the brain must submit the muscle to a preparation without which the organ of movement would not be ready to obey without loss of time.

To elucidate this point we need a rather subtle analysis which will be best performed with the aid of an example.

In a fencing-bout two fencers will sometimes watch each other closely for several minutes without making any movement. All at once this immobility gives place

to an exceedingly rapid movement: one of the fencers has seen daylight, that is a space of a few millimetres which the other had discovered by an imperceptible displacement of his hand, and the foil, moving with all possible speed at the very moment this opportunity was given, strikes him full in the chest. This is one of the most valued thrusts in fencing, and those who perform it successfully are reputed to have readiness in attack.

What happens in this very short space of time necessary for the delivery of a direct blow? The fencer has uncovered himself, his opponent judges that he can reach him; in a moment the muscles contract and the weapon reaches its mark.

There is nothing more easy in appearance than this movement of stretching the arm out straight, while the legs violently thrust the body in the direction of the blow. But this simple blow which needs neither cunning feints nor delicacy of touch, and which only consists in a straightforward extension of arm, is really one of the most difficult attacks of fencing. Like a cat lying in wait for a mouse, the fencer who is watching his opponent must seize for attack the precise instant when the opportunity occurs, or his chance will be lost. A man must be a fencer himself in order to understand the value of an infinitesimal fraction of a second when he has to make a thrust the very moment a chance is given him the conception of the blow and its delivery must both occur in the duration of a flash of lightning.

We call the sudden extension of the leg which throws forward the fencer's body, and the quick movement of the arm which directs his foil against his opponent, a lunge. Now this movement cannot take place without an almost instantaneous obedience of the muscles to the' will. We call the aptitude of a fencer for passing instantaneously at the right moment from absolute immobility to the most rapid movement, his quickness. Fencers who are deficient in quickness can calculate a blow, and can recognise the precise instant when it ought to be delivered, but the arm and leg do not obey quickly enough. The blow may have been conceived in

time, but it is delivered too late. "Quickness" of the muscles and instantaneous movements need a considerable nervous expenditure, of which certain physiological facts give us an explanation.

A muscle does not instantaneously obey the order of the will. This discovery was made clear by Helmholtz in 1850. This physiologist showed that when a given point of a motor nerve receives an electric stimulus an appreciable interval occurs between the moment of stimulation and that of contraction. This retardation in the muscle is partly due to the time occupied by the stimulus in traversing the nerve; but taking into account the duration of this, which can be exactly measured, we find that there remains an appreciable fraction of time in which the muscle which has already received the stimulus has not yet begun to contract. Helmholtz gave the name of latent period to this silent time in which the motor organ, having already heard the call of the will, has not yet responded by a movement.

Now, various circumstances can alter the duration of the latent period, and render more or less speedy the obedience of the muscle to the stimulus which it receives. The most efficacious condition for shortening the latent period is increase of the strength of the stimulus,

Let us suppose that the motor organ is stimulated by an electric current. The latent period being two hundredths of a second with a current of known intensity, its duration will be reduced to one hundredth of a second if we double the intensity of the current.

If the muscle is stimulated by the Will, the same law will be applicable to the duration of the latent period, and this will be shorter in proportion as the strength of the voluntary stimulus is greater, this increase of the stimulus being represented by a more violent disturbance in the nerve-cells and fibres. The Effort of Will will then be more intense according to the suddenness with which the movement has to be performed, whatever the speed of the actual movement and the intensity of the muscular effort which determines it.