VELOCITY AND DELICACY OF MUSCULAR ACTION.

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energy of metamorphosis is greater. Hence the mechanical effects of smaller fibres is heightened, "just as a bundle of magnets has a greater effect than one massive magnet of the same weight." The force of the muscle of mammals is hence greater than that of the frog.

The remarkable duration and sustentation of muscular effort in birds thus also finds satisfactory explanation. Montague, a celebrated ormithologist, estimates that hawks fly at the rate of 150 miles an hour and various birds often travel 600 to 1000 miles without food in their winter and summer migrations. But it is in insects, in which the muscle caskets have been discovered to be minute structures distinctly suspended in fluid, that the force of contraction is greatest in proportion to their size. Thus Dunglison states that the lucanus cervus, or stag-beetle, has been known to gnaw a hole, of an inch diameter, in the side of an iron canister in which it had been confined, and the same author calls attention to the persistence and apparent ease with which flies will keep up with the fleetest race horse, sweeping large circles about him all the time. The stridulations (scrapings of wing covers) made by crickets and grasshoppers can be heard a mile, whence it is estimated that if man could emit sounds whose intensity should be proportionate to his size, he could make himself heard all around the earth.

The Velocity and Delicacy of Muscular Action.

We may not take final leave of the properties of muscle without calling attention to the readiness of its response to stimulus, its capacity for swift repetition of contraction, and the degree of delicacy and accuracy of its action under proper cultivation. The ready response of muscle has been clearly shown by Kronecker and Stirling in their demonstrations that muscle replies to stimuli, which reach their

222 VELOCITY AND DELICACY OF MUSCULAR ACTION.

maximum in the nerve in less than the 5000 part of a second. And as to the capacity for swift repetition of contraction, these same experimenters quote the observations of Ranvier, who remarked that the pale muscle of the rabbit could indicate 357 single contractions in a second, and of Marey that the common horse-fly can make voluntarily 330 movements of the wing in a second. The musical tone emitted by the contraction of muscle gives an accurate estimate of the rapidity of muscular movement. A certain tone corresponds, of course, to a certain number of vibrations, and hence it is calculated that the wings of insects strike the air even many thousand times every second. The finest muscular movements in man, are those which change the position and tension of the vocal cords. Müller has observed that there are at least 240 different states of tension of the vocal cords, and as the whole variation is not more than one-fifth of an inch, the variation required to pass from one interval to another will not be more than 200 of an inch.

The quick, deft and delicate play of muscles is hardly anywhere better exhibited in man than in the modulations of the voice, in the shades of expression of the face, and in the infinite variety of gesticulation. Thus:

"The arched and polished forehead," says Sir Charles Bell, "terminated by the distinct line of the brow, is a table, on which we may see written in perishable characters, but distinct while they continue, the prevailing cast of thought." "You may sometimes trace

A feeling in each footstep, as disclosed
By Sallust in his Cataline who, chased

By all the demons of all passions showed

Their work even by the way in which he trode." Byron.

NERVE AND ITS PROPERTIES.

223

LECTURE XI.

NERVE AND ITS PROPERTIES.

CONTENTS.

The Prime Function of Nervous Tissue-Subordination to Other Tissues -Independence of Nerve Force-Genesis of Nerve Force-Arrangement of Nerve Tissue-White and Gray Matter-The Cerebro-Spinal and Sympathetic Systems-The Nerve Cells-The Nerve FibresThe Neurilemma-The Axis Cylinder-The Gray Fibres-The Properties of Nerves-Terminations of Sensitive Nerves-Terminations of Motor Nerves-Course of Nerve Fibres-Identity of Nerve Fibres -Indifference of Direction of Nerve Force-The Chemistry of Nerve Tissue-The Action of Electricity upon Nerve Tissue-The Nature of Nerve Force-Rate of Conduction of Nerve Force-Nerve Force and Electricity-Comparative Velocity of Nerve and Other Forms of Force-The Reception and Perception of Impressions-Ancient Significance of Nerves-The Effects of Use, Disuse and Age.

The primary object of the nervous tissue is to link together different and often widely distant structures. The nervous system is thus the supreme regulator of the actions of the body. It secures harmonious and consentaneous, or coördinated, operations. Thus, if muscular activity is to be increased (exercised), the muscle substance must needs have more fuel in the way of additional supply of blood; it must also have more oxygen to effect the consumption of the fuel and thus the liberation of additional force. Hence increased muscular activity implies accelerated circulation and accelerated respiration. It is the function of the nervous system to secure this consentaneous and correspondent activity on the part of the heart and lungs as well as on the part of the muscle. The nervous system has, at the same time, to regulate the activity of the secretory organs to provide for the escape of the products of combustion. Complexity of organisation implies, therefore, a nervous

224 THE NERVOUS, SUBSIDARY TO OTHER TISSUES.

system in high degree of development. An animal takes rank in the animal scale, according to the degree of development of its nervous system, that is, according to the quantity and quality of its nervous tissue.

The Nervous, Subsidary to Other Tissues.

But so much stress has been laid upon the supremacy of the nervous system that we are apt to forget that the rest of the animal was not constructed for the nervous system; the nervous system is constructed rather for the benefit of the animal. In fact, the nervous system stands towards the rest of the body, much in the light of telegraphy to the inhabitants of a country. It signalises wants and supplies, regulates transmissions, warns of dangers and furnishes intelligence. We look back with a feeling of pity and contempt, upon that state of society which enjoyed no system of telegraphy, no means of rapid communication, just as we look down upon animals not endowed with nervous tissue, yet we may not forget that such states of society, and such kinds of animals, did and do exist. The nervous system is thus an addendum to a higher grade of development. We may not, therefore, look upon the body as a collection of cells attached to the nervous tissue like the leaves, for example, upon the trunk and twigs of a tree. On the contrary, it is the nervous system which is attached to the cells. The nerve fibres are to be looked upon as offshoots from the cells for the purpose of association and interaction.

Independence of Nerve Force.

It was once believed, is taught now by some metaphysicians, that nerve force is born in nerve centres and is sent through nerve fibres to muscles, for instance, where it acts as motion. That is, that motion is only a transformed nerve force. But the physiologist can not accept such a

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doctrine. The nerve force is not the fuel for the muscle. The blood, which is the prepared food, is the fuel that furnishes the muscle with force. The nerve force is simply the excitant of the muscle. A very small amount of nerve force suffices to induce a very great amount of muscular force. Muscle is a machine, as we have seen, like an engine. It stands ready to act. There is steam in the boiler, that is, there is blood in its substance. Still the engine does not move. The nerve force is the hand that opens the throttle 'and thus causes the machinery to move. I might make this point plainer by likening the parts of the body to different branches of a great army out upon the field. The nervous system is the system of telegraphy which directs the movements of the army. But no one would claim that the movements of the army, were transformations or transubstantiations of the force of electricity in the battery of the telegraph.

Genesis of Nerve Force.

The nerve force is generated in nerve cells and is conducted along nerve fibres or tubes. The study of the nervous system divides itself, thus, physiologically, into the study of the generators and the conductors. Cells never conduct and fibres never generate. Of course, in using the term generate, it is not meant to imply the creation of a new force. Such a conception is unscientific, that is, false. The nerve cells generate nerve force in the sense in which the cups of a galvanic battery generate electricity. The electricity from galvanism is the result of chemical force which, in turn, is liberated from force latent in metals, etc., stored up in the past. So the nerve cells are simply means of transforming latent force in the blood into nerve force. We return again to the galvanic battery.