But if we make this calculation exactly and then compare the results with those given by direct observation, we discover that the contraction of the muscle is retarded. An appreciable interval separates the instant at which the stimulus of the will reaches the muscle, and the instant at which the latter responds by a contraction.

This period, during which the already stimulated muscle has not yet begun to contract, is known as the period of latent contraction.

The period of latent contraction is not always of the same duration. Many circumstances may cause a variation, but increased intensity of the stimulus received by the muscle is the condition which most efficiently shortens the latent period. To a feeble stimulus, the muscle responds slowly, lazily; an energetic shock on the other hand is followed by a prompt contraction.

It was established by Helmholtz as a physiological law, that, the length of the latent period is in inverse proportion to the intensity of the stimulus received by the muscle.

When the will orders a muscle to contract, the latter obeys the more promptly, the more violent the nervous disturbance which transmits the order.

We shall see later what we shall deduce from these physiological data for the explanation of the great waste of nervous energy brought about by certain exercises which only represent a moderate expenditure of muscular energy, but which demand an instantaneous obedience of the muscles to the orders of the will: fencing for example.

CHAPTER II.

MOVEMENTS.

Associated Action of Different Regions during Work-How Blow is given with the Fist-Coordination of Movements; Antagonistic Muscles; the Muscular Sense-Ataxic PatientsStatic Contraction-Stiffness in Exercises-Muscular Education. Association of the great Organic Functions with Muscular Movement-Effort-The Porter and his Load— Effort during Slight Expenditure of Force; too Hard a NutFrequency of Effort in Exercise-Long-Distance and Sprint Running. Influence of Movements on the Circulation-The Quickening of the Pulse; its Mechanism-The Pulmonary Circulation and the Active Congestion of the Lungs-Congestion of the Brain during Movement-Dancing DervishesA Runaway Horse.

I.

THE slightest movement performed by the human machine needs the employment of a great number of wheels. When a muscle contracts, the neighbouring muscles always, and distant ones sometimes, act with it, and are associated in its work.

Let us analyse the phenomena of a very simple movement.

In order to be able to move the forearm, the arm must be fixed to give a point of application. The arın itself must be supported by the shoulder, and the shoulder by the vertebral column and the thorax. the thorax and vertebral column being supported by the pelvis, and this by the lower extremities, the whole body is obliged to associate in the movement of the forearm. From head to foot, all the muscles participate in the most insignificant, and most localised work.

The slightest movement has a tendency to displace the centre of gravity of the body. While the extremities are at work, the vertebral column, a long bony rod which forms the axis of the body, oscillates like the beam of a balance, to right or to left, forwards or backwards, to compensate for the displacement occasioned by the burthen raised or the movement performed.

The lower limbs almost always associate in the movements of the upper limbs, and in many cases, a man really derives from his legs the force which seems to come from his arms.

"When I had my two legs," said a Zouave from whom they had been cut off, "I used to give a splendid blow with my fist!" And the Zouave was right. A well delivered blow with the fist is supported by the whole body. The effort which thrusts forward the closed hand begins in the leg, which is extended, and then involves the thigh which projects the trunk in the direction in which the blow is delivered; the muscles of the loins. transmit the movement to the thorax, and those of the thorax pass it on to the shoulder, which in its turn thrusts forward the forearm and the fist, transmitting to them the force to which the whole body has contributed.

In this manner every muscular movement may have an influence at a point very far distant from that to which it seems to be localised. Hence an exercise sometimes produces very marked effects in a region of the body in which we should not have dreamed of looking for them.

The muscles of a whole limb almost always act all together in the performance of a movement, although in each limb one half of the muscles generally has an action diametrically opposed to that of the other half. In the forearm, the muscles of the anterior surface have the function of flexing the fingers and closing the hand; they are flexors. Those of the posterior surface are extensors, and the action is to open the hand. For this reason these two sets of muscles are called antagonists.

In the performance of a movement, no muscle ever

acts without a corresponding contraction of its antagonist, which submits it to a kind of balance and control. This opposition is necessary to moderate, direct, and make accurate the movement.

When two men are wheeling a barrow down a hill, and the one in front pulls forwards, and the one behind backwards, we may say that the action of the first is antagonistic to that of the second. Their efforts in different directions are combined in order that the barrow may advance neither too slowly nor too quickly, and may go at a uniform pace. In the same way two antagonistic muscles regulate each other; when they oppose each other in a proper measure, the movements are precise and well co-ordinated.

Co-ordination of movements is perfected by exercise, but it is often instinctive and perfect from the time of birth in the performance of certain natural actions. The chicken hardly out of the egg, reaches with the first stroke of its beak the grain of corn it sees, and the infant needs no practice to learn the degree of contraction of the lips and tongue necessary in the act of sucking.

For the movements of an exercise, however, it is sometimes necessary to go through a long apprenticeship. Much practice is necessary before a pianist is able to place his finger on the desired note with an ease equal to that which the chicken puts its beak to a grain of corn. Thanks to the muscular sense we can educate antagonistic muscles, and succeed, after more or less practice, in making them act with perfect harmony.

The muscular sense is the feeling we have of the force with which a muscle contracts and the direction in which it acts. It is the muscular sense which enables us to place the hand or the foot on the precise point which we wish to touch. By means of it we regulate the expenditure of muscular force in proportion to the resistance to be overcome. This sense guides us independently of vision, and enables us to reach, with our eyes closed, objects the position of which is exactly known to us different parts of our body, for instance.

There is a disease characterised by the abolition of the muscular sense, and by defective co-ordination of movements; this is locomotor ataxy. The ataxic man does not know how to give to his muscles an impulse suitable to the movement required. If he wishes gently to take up an object, his hand passes by it, or strikes and upsets it. If he wishes to walk a few steps, his legs are violently projected forwards, to the side, or upwards. He has the aspect rather of an individual desirous of kicking someone with his foot, than of one who wishes to walk.

A nimble man, by the use of his muscular sense, can perform the most surprising feats. The skill of jugglers and balancers is due to the cultivation of this sense, and to the education of antagonistic muscles.

In all forms of bodily exercise, antagonistic muscles play a most important part, and it is impossible to understand certain phenoniena of fatigue, without taking their action into account. Just as much as antagonistic muscles facilitate movement when their action is exact and moderate, so much can they hinder it when they act in an exaggerated or unsuitable manner.

Let us suppose that the flexors and extensors of the arm contract with an equal energy, the limb drawn by two equal forces in two opposite directions will remain motionless. We can easily understand that this immobility is not that of repose. It is contracture or static contraction, so called in contradistinction to the dynamic contraction which accompanies movements. It has been proved that static contraction produces greater fatigue, and causes a more immediate rise in the temperature of a muscle than dynamic contraction.*

In common language, static contraction is called stiffness. In bodily exercises, exaggerated and ill-planned contractions of antagonistic muscles produce stiffness of the movements. It is the fault of all beginners, and the sign of inexperience in skilled labour. "Don't keep your fingers so stiff," we say to a young pianist. "Your

Béclard. Physiologie.