CHAPTER I.

OF SPONTANEOUS ACTIVITY AND THE FEELINGS OF

MOVEMENT.

1.

THE

HE feelings connected with the movements of the body or the action of the muscles, are now recognized as a distinct class, differing materially from the sensations of the five senses. They are often regarded as proceeding from a Sense apart, a sixth, or Muscular Sense, and have accordingly been enrolled under the general head of sensations. That they are to be dealt with as a class by themselves, no less than sounds or sights, love, irascibility, or the emotion of the ludicrous, is generally admitted.

With regard, however, to the position of this class of feelings in the plan or arrangement of our subject, there is still room for differences of opinion. In my judgment they ought not to be classed with the Sensations of the five Senses; and I believe further that the consideration of them should precede the exposition of the Senses. The reasons for this opinion are the two following :-namely, that movement precedes sensation, and is at the outset independent of any stimulus from without; and that action is a more intimate and inseparable property of our constitution than any of our sensations, and in fact enters as a component part into every one of the senses, giving them the character of compounds while itself is a simple and elementary property. These assertions require to be proved in detail, but before doing so, it is advisable to notice briefly the mechanism or anatomy of movement in the animal frame.

OF THE MUSCULAR SYSTEM.

2. Muscular Tissue.-'The muscular tissue is that by means of which the active movements of the body are produced. It con

sists of fine fibres, which are for the most part collected into distinct organs, called muscles, and in this form it is familiarly known as the flesh of animals; these fibres are also disposed round the sides of cavities and between the coats of hollow viscera, forming strata of greater or less thickness. The muscular fibres are endowed with contractility—a remarkable and characteristic property, by virtue of which they shrink or contract more or less rapidly under the influence of certain causes which are capable of exciting or calling into play the property in question, and which are therefore named stimuli. A large class of muscles, comprehending those of locomotion, respiration, expression, and some others, are excited by the stimulus of the will, or volition, acting on them through the nerves; these are therefore named 'voluntary muscles,' although some of them habitually, and all occasionally, act also in obedience to other stimuli. There are other muscles or muscular fibres which are entirely withdrawn from the control of the will, such as those of the heart and intestinal canal, and these are accordingly named 'involuntary.' These two classes of muscles differ not only in the mode in which they are excited to act, but also to a certain extent in their anatomical characters.'-SHARPEY; QUAIN'S Anatomy.

Structure of Voluntary Muscles.-The voluntary muscular fibres are for the most part gathered together into distinct masses, or muscles of various sizes and shapes, but most generally of an oblong form, and furnished with tendons at either extremity, by which they are fixed to the bones. The two attached extremities of a muscle are named, in anatomical descriptions, its origin and insertion, the former term being usually applied to the attachment which is considered to be most fixed, although the rule cannot always be applied strictly. The fleshy part is named the belly.

'The muscular fibres are collected into packets or bundles of greater or less thickness, named fasciculi, or lacerti, and the fibres themselves consist of much finer threads visible by the aid of the microscope, which are termed muscular filaments, or fibrillæ.

'The fibres, although they differ somewhat in size individually, have the same average diameter in all the voluntary muscles, namely, about of an inch; and this holds good whether the

muscles be coarse or fine in their obvious texture. According to Mr. Bowman their average size is somewhat greater in the male than in the female, being in the former and in the later, or more than a fourth smaller.'-Ib.

'As to the structure of fibres, it has been ascertained that each is made up of a larger number of extremely fine filaments or fibrils, inclosed in a tubular sheath.' 'It would seem that the elementary particles of which the fibril is made up, are little masses of pellucid substance presenting a rectangular outline, and appearing dark in the centre.' 'The length of the elementary particles is estimated by Mr. Bowman at go of an inch. He finds that their size is remarkably uniform in mammalia, birds, reptiles, fishes, and insects.'-Ib.

Nerves of Voluntary Muscles.—The nerves of a voluntary muscle are of considerable size. Their branches pass between the fasciculi, and repeatedly unite with each other in form of a plexus, which is for the most part confined to a small part of the muscle, or muscular division in which it lies. From one or more of such primary plexuses nervous twigs proceed and end by finer or terminal plexuses, formed by slender bundles consisting of two or three primitive tubules each, some of them separating into single tubules.-Ib.

'By means of the microscope these fine nervous bundles and single tubules may be observed to pass between the muscular fibres, and after a longer or shorter course, to return to the plexus. They cross the direction of the muscular fibres directly or obliquely, forming wide arches; and on their return they either rejoin the larger nervous bundles from which they set out, or enter into other divisions of the plexus. The nervous filaments, therefore, do not come to an end in the muscle, but form loops or strings among its fibres.'-Ib.*

I refrain from entering into the description given of the involuntary muscles,-those of the heart, intestines, bronchial tubes, iris, middle coat of the arteries, &c.-as being less important for the object of the present work. It will, how

The active connexion between the nerves and the muscles would seem to consist in an electrical current passing from the one to the other. The numerous experiments of Du Bois Reymond and others in this subject, scarcely permit any other conclusion.

ever, be interesting to hear what the same authority has said on the Sensibility of muscle, and also on the Contractility, or the source of its power as a mechanical prime mover.

3. Sensibility. This property is manifested by the pain which is felt when a muscle is cut or lacerated, or otherwise violently injured, or when it is seized with spasm. Here, as in other instances, the sensibility, properly speaking, belongs to the nerves which are distributed through the tissue, and accordingly, when the nerves going to a muscle are cut, it forthwith becomes insensible. It is by means of this property, which is sometimes called the 'muscular sense,' that we become conscious of the existing state of the muscles which are subject to the will, or rather of the condition of the limbs and other parts which are moved through means of the voluntary muscles, and we are thereby guided in directing our voluntary movements towards the end in view. Accordingly, when the muscular sense is lost, while the power of motion remains,—a case which, though rare, sometimes occurs,-the person cannot direct the movements of the affected limbs without the guidance of the eye.'

On this passage I would remark that the two sensibilities described differ very much in their character. The sensibility to injuries is a fact distinct from those feelings of the state of voluntary muscles that serve to guide the movements in working for ends. The one is the passive, and the other the active, sensibility of muscle.

4. Irritability or Contractility.—' In order to cause contraction, the muscle must be excited by a stimulus. The stimulus may be applied immediately to the muscular tissue, as when the fibres are irritated by a sharp point; or it may be applied to the nerve or nerves which belong to the muscle; in the former case the stimulus is said to be "immediate," in the latter "remote." The nerve does not contract, but it has the property, when stimulated, of exciting contractions in the muscular fibres to which it is distributed, and this property, named the "vis nervosa' (true nervous force), is distinguished from contractility, which is confined to the muscle. Again, a stimulus may be either directly applied to the nerve of the muscle, as when that nerve is itself mechanically irritated or galvanized; or it may be first made to

THE STIMULI TO MUSCLES.

63

act on certain other nerves, by which its influence is, so to speak, conducted in the first instance to the brain or spinal cord (or perhaps even to some subordinate nervous centre) and thence transferred or reflected to the muscular nerve.

'The stimuli to which muscles are obedient are of various kinds; those best ascertained are the following, viz. :-1. Mechanical irritation of almost any sort, under which head is to be included sudden extension of the muscular fibres. 2. Chemical stimuli, as by the application of salt or acrid substances. 3. Electrical; usually by means of a galvanic current made to pass through the muscular fibres, or along the nerve. 4. Sudden heat or cold. These four may be classed together as physical stimuli. Next, mental stimuli, viz.-1. The operation of the will, or volition. 2. Emotions, and some other involuntary states of the mind. Lastly, there still remain exciting causes of muscular motions in the economy which, although they may probably turn out to be physical, are as yet of doubtful nature, and these, until better known, may perhaps, without impropriety, be called organic stimuli; to this head may be also referred, at least provisionally, some of the stimuli which excite convulsions and other involuntary motions which occur in disease.'-p. clxxvii.

Of the stimuli thus enumerated the most interesting to us are the mental stimuli. These are described as of two kinds; the Emotions-or the influence of the Feelings-and the Will. A third kind is the Spontaneous force to be presently discussed. There is one other property of muscle, alluded to in the previous chapter, which is described as follows:

5. Tonicity or Tonic Contraction.- Although in muscles generally, contraction is succeeded by complete relaxation, there are various muscles which, after apparently ceasing to contract, remain in a state of tension, and have still a certain tendency to approximate their points of attachment, although this tendency is counterbalanced by antagonistic muscles, which are in the same condition, and the limb or other moveable part is thus maintained at rest. This condition of muscle is named "tonicity," or the "tonic state." It is no doubt a species of contraction, as well as the more conspicuous and powerful action with which it alternates; but it is employed merely to maintain equilibrium, not to cause motion, and it is not temporary but enduring-con