CLASS IV. NEUROTICA. ORDER III. CINETICA. Biseases affecting the Muscles. IRREGULAR ACTION OF THE MUSCLES OR MUSCULAR FIBRES; COMMONLY DENOMINATED SPASMS. ORDER III. General character of muscular massy form. fibres in a HAVING, in the Physiological Proem to the present class, CLASS IV. glanced, as far as our space would allow, at the disputed question concerning the nature of muscular irritability, or contractility, to adopt the language of Dr. Bostock, and its affinity with sensorial or nervous influence, it is now only necessary at present to take a very brief view of the general character and mode of action of muscles as they appear to the naked eye in a massy form, or, in other words, as composed of an almost infinite variety of minute fibres. muscular action upon themselves. A muscle thrown into action, increases in absolute Effects of weight, in density, and in power of resistance. It is also said to increase in absolute bulk; but the experi- muscles ments upon this subject are contradictory; the middle or belly of the muscle, indeed, is at this time evidently enlarged, but then its length appears to be proportionally CLASS IV. diminished. ORDER III. Diseases af- Approxi mate the nature of Muscles constitute the cords, as bones do the levers, of the living frame; and in most cases the muscles grow tendinous, as the bones do cartilaginous, towards their extremities; by which means the fleshy and the osseous parts of the organs of motion become assimilated and fitted for that insertion of the one structure into the other upon which their mutual action depends; the extent and nature of the motion being determined by the nature of the articulation, which is varied with the nicest bones as the skill to answer the purpose intended. Whether, however, the substance of tendons consists of the same fibres as the belly of a muscle but only in a state of closer approximation and possessed of finer vessels which do not admit the introduction of red blood, or whether they form a distinct system of fibres, merely attached to those of the muscles, is at present undecided. It is certain that tendons possess nothing of the peculiar structure of muscles, and seem to be more nearly allied to the simple solid*. latter do of muscles at their extremities. Structure of tendons. Though more com pact than muscles often broken by their exertion. It appears singular, at first sight, that the tendinous fibres which thus seem to be compacted into a firmer and more substantial cord than those of the muscles, should be sometimes broken by muscular exertion, while the muscular fibres remain uninjured; yet this unquesExplained. tionably depends upon their greater rigidity, and, consequently, inability of yielding to the force by which they are opposed. And hence it is that the bones themselves are sometimes broken in the same manner, as by a violent jerk, or a sudden and spasmodic contraction, of which we shall presently meet with examples, especially in the patella, the ribs, and the arms. The muscles themselves, however, are occasionally ruptured by a like irregular violence and excess of power, as the recti abdominis in tetanus, and the gastrocnemii in cramps. Bones sometimes broken in the same manner. Muscular action produced by a principle peculiar to life: Muscular action, then, consists in a mutual attraction and concentration of the constituent fibres of muscles, in a manner peculiar to living matter, for we cannot * See Dr. Bostock's Elementary System of Physiology, p. 67, 8vo. 1824. CLASS IV. ORDER III. Cinetica. imitate it by any combination or action of mechanical fibres. It is not, however, a contraction in every dimension, since in this case the muscular volume would Diseases afbe diminished; but in length only, attended with a profecting the portional increase of bulk, so as to preserve the absolute volume unchanged, or nearly so. muscles. enormous: but over rated by the me It is easy to conceive, from these few remarks, that Its force the force exerted by muscular contraction may be enormous; but by the mechanical physicians it was calculated in the most extravagant manner from premises in many chanical instances wholly chimerical. Thus Borelli estimated the physicians. force with which the heart contracts, in order to carry Singular forward the circulation of the blood, to be equal to not miscalculaexamples of less than 180,000 lbs. at each contraction; while Pitcairn, tion. applying the same speculation to the function of digestion, conceived that this process is accomplished by a muscular exertion divided equally between the stomach and the auxiliary muscles that surround it, amounting in the stomach alone to the force of 117,088 lbs. for which had he assigned five ounces," says Professor "he would have been nearer the truth." Monro, Yet we do not want these visionary calculations to prove the wonderful power possessed by muscular fibres; the facts we have already adverted to, and others we shall have to notice in the course of the present order, are sufficient to establish their astonishing energy, without having recourse to unfounded hypotheses, or exaggerated statements. 99 In general, says Dr. Parr, in a very excellent article upon this subjectt, it appears that the force with which a muscle contracts is in proportion to the number of its fleshy fibres, and the extent of the surface to which these fibres are attached; but its degree of contraction or the extent of its motion is in proportion to their length. The limits of contraction differ in the long and in the Law of circular muscles; for the former do not contract more contraction: than one third of their length, but the circular fibres of * Monro, Comp. Anat. Pref. p. viii. + Med. Dict. in verb. Musculus. muscular as exhibited in the long and circular muscles. ORDER III. Diseases af CLASS IV. the stomach, which in their utmost dilatation may be expanded to a foot in circumference, may, after much fasting, be reduced to the circle of an inch. It must, however, be added that in circular muscles no fibres pass completely round; bundles of fibres are collected and end at different points, while some begin where others end. Each may, therefore, admit of only a limited contraction, while the dilatation just mentioned may be the sum of the whole. Action of muscles mitted but only diminished ever in sleep. Why in this state the flexors the exten sors. The action of muscles is never intermitted, and only never inter- diminished in the sleeping state; though where the sleep is profound and lethargic the diminution amounts to almost a cessation, except in the voluntary organs. When muscles are not exercised, the sensorial or irritable fluid moves forward with an easy flow; or in the words of Haller "the vis insita is very slightly exerted"; but we can still trace its influence by the position which the limbs assume and discover the relative strength of the antagonising muscles. Thus we find the flexors stronger than the extensors; for, during sleep, the head falls forward, and the body, legs, arms, and fingers are slightly bent. The cause of this additional strength is easily explained; for overbalance the flexors have stronger and more numerous fibres; their insertion is farther from the centre of their motions, and Illustrated. under a larger angle, which must increase when flexion has begun. This superiority of the flexors bends the fetus in the womb into a round ball. The same superiority of power continues, though in a less degree, after birth, and hence frequent pandiculations are required to give activity and energy to the extensors, which they again lose in advanced age. On awaking from a sound sleep the same yawnings and stretchings occur from the same cause and Bethel fancifully refers the crowing of the cock and the fluttering of his wings to a similar purpose. It is always useful in diseases to examine the position of the limbs during sleep, particularly the sleep of children. If they deviate from the ordinary degree of flexure to a more straight position, there is generally some irregularity in the state of tone, and of course in the vital influx. This doc trine of use in symptomatology. CLASS IV. Cinetica. ORDER III. muscles. distinct The irritability or contractility of a muscle is a very different power from that of elasticity. The latter always depends upon simple re-action, and is never a source of Diseases afactual energy: it merely restores, in a contrary direction, fecting the the force which had been impressed, and the effect which Contracit produces can never be greater than the amount of the tility widely cause. But in muscular contraction the mechanical ef- from fect produced is infinitely greater than the mechanical elasticity, Compared. cause producing it, as when the organ of the heart recently detached from the body just dead is slightly scratched in its inside by a needle, it will contract so strongly as to force the point of the needle into its substance*. But the chief proof of the difference between the two is that the irritable power of a muscle is often excited without any mechanical cause at all, and from the mere influence of the will, which has no effect upon the simple elasticity of organs. Hence, while contractility belongs to the muscular structure alone, elasticity appertains to many other substances as well, whether animal, vegetable, or even metallic. Muscles also have their elasticity, but the principle is altogether of a different kind, though often confounded with the preceding by modern pathologists; and particularly in their use of the term tonicity, Tonicity which is often employed with little precision, and frequently means nothing more than this common principle of elasticity, to which indeed it seems directly to be applied by Dr. Cullen. often used synonym ously with elasticity. or animal or auto The muscles of the body may be divided into two Voluntary grand classes, voluntary or animal, and involuntary or muscles as automatic. In the former we meet with some that are contradistinguished peculiarly remarkable for strength and continuity of con- from intraction, as the greater part of the round muscles; and voluntary others as remarkable for mobility and vacillation; among matic. which we may place most of the long muscles. These Distinctive properties are strikingly exemplified in a state of disease, characters. and call for particular attention; the muscles characterized by mobility presenting examples of atonic or agitatory Fordyce, Phil. Trans. 1788, p. 80. + Bostock, Elem. Syst. of Physiology, p. 168, 8vo. 1824. |