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'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.

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'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 332, and in the latter, 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.' 'When a fibril completely insulated is highly magnified, it is seen to consist of a single row of minute particles, connected together like a string of beads.' 'The length of the elementary particles is estimated by Mr. Bowman at 4 of an inch, while their transverse diameter is less, often by one-half, at least, in specimens which have not been altered by contraction, 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 in their progress repeatedly unite with each other in form of a plexus, the finer branches of which may be seen running between the smallest order of fasciculi, often in company with blood vessels; at last the nervous plexus is reduced into minute bundles consisting of two or three primitive tubules each, some of them separating into single tubules. 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 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. clxxii.

I refrain from transcribing 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, however, be interesting to hear what the same authority has said on the Sensibility of muscle, as well as on the contractility, or 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, 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.'—p. clxxvii.

On this passage I would remark that two very different modes of muscular sensibility are here indicated, while a third mode distinct from both is omitted. In my view the feelings arising from wounds, lacerations, injuries, and spasms make one class; the feelings of pleasure, and sometimes of pain, arising from movement, exercise, and resistance are a second class; and the conscious states that act as guides to the voluntary movements constitute a third class. Between the first and third, those given above, as almost the same, there is a very wide distinction, not to say a strong contrast; while the pleasures of exercise and activity which have their seat in the muscles, the class overlooked in the foregoing quotation,

MUSCULAR STIMULI.

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are considerably different from either. The detailed illustration of these various kinds of sensibility will be given before concluding the present chapter.

With regard to the other property of muscle, I shall likewise quote from the same source.

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 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 a certain length, however short, of the nerve; the effect taking place on closing or on breaking the circuit. 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. Inverting the order, we should say, first, that it is a property of the emotions to excite the muscles into action, a proposition which will be maintained in a very extended form throughout this work; and, secondly, that there is a class of actions distinct from the immediate promptings of emotion, and yet related to emotion; these are the actions of the will, or volition, which I consider to be nothing else than action stimulated, and guided, by feeling. There is one other property of muscle, which has been alluded to in our previous chapter, but from the importance to be attached to it in the discussion that is to follow, I quote a paragraph referring to it. The title is

5. Tonicity, or Tonic Contraction.- Although we say that contraction of a muscle is succeeded by relaxation, it must not be supposed that, during the intervals of repose, the muscle is inert and flaccid. On the contrary, it is still in a state of tension, and has still a certain tendency to approximate its points of attachment, although this tendency is counterbalanced by antagonist 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, continuing during sleep, when volition is in abeyance, and occasioning no fatigue. It appears to be excited through the medium of the nerves, though independently of the will, for when the nerves are cut it ceases, and then the muscles nearly become flaccid: the stimulus which acts on the nerves is not known.'-p. clxxxii.

We have already remarked, in speaking of the functions of

PROOFS OF SPONTANEOUS ACTIVITY.

73 the spinal cord, considered as a centre, that this tonicity of the Lerves must be looked on as one of those functions; for the moment the spinal cord is destroyed the limbs of an animal become entirely flaccid. We also remarked, that this is an instance to prove that a muscular stimulus may originate in a centre and keep flowing out from that centre, without reference to any impressions derived from without, although the existence of such impressions, or the presence of emotion of any kind, determines a special flow of stimulus from the different centres or grey deposits of the brain and spinal cord. The use to be made of this observation will presently appear.

PROOFS OF SPONTANEOUS ACTIVITY.

6. We have now to consider the evidence that there is for the existence of a class of movements and actions, anterior to, and independent of, the sensations of the senses. This question, brought on here to settle a point of precedence or arrangement, has a far wider import, and will reappear on various occasions in the course of our subsequent exposition.

The proofs principally to be relied on are the following:(1.) The already mentioned fact of the tonicity of muscles. This fact I regard as proving the existence of a central stimulus in the nervous system, or that the centres possess an initiative in the phenomenon of muscular movement. It is true that the tonicity does not amount to actual movement, but the tension implied in it is only a lower degree of the same thing: and what one centre does in a low degree another may do in a higher; the peculiar mode of operation is established as a fact of the nervous mechanism.

(2.) The permanent closure of certain of the musclesthose named sphincters-is an effect of the same nature as the tonicity, but displaying a more energetic stimulus still-a stimulus that we can refer only to the spontaneous influence of some one of the centres. No impression from without, or from within the body, can be pointed out as originating this contraction. Neither could the closure be maintained by the muscle's own contractility, which, as before remarked, may