194 THE EXERCISE OF THE MUSCULAR SENSE. different muscles in all the voluntary and involuntary acts of the body, in assuming and maintaining its different positions, as in standing, walking, balancing, dancing, riding, swimming, etc.; in executing the finer movements of the handicrafts, playing upon musical instruments, etc.; in arranging the features and changing the expression of the face and members in the infinite variety of gesticulation; in the quick movements of the eye, and, finest and nicest of all, in the delicate modulations of voice and speech. So it was no wonder that Sir Chas. Bell, the eloquent English anatomist, could not restrain himself after observing the fineness and nicety of the action of the muscular sense, from expressing his admiration in a fitting tribute of praise. "When," he exclaims, "a blind man or a man blindfolded, stands upright, neither leaning upon or touching aught, by what means does he maintain his erect position? The symmetry of his body is not the cause. A statue of the finest proportion must be soldered to its pedestal, or the wind will cast it down. How is it, then, that a man sustains the perpendicular posture or inclines in the due degree towards the wind that blows upon him? It is obvious that he has a sense by which he knows the inclination of his body; and that he has a ready aptitude to adjust the parts of it so as to correct any deviation from the perpendicular. What sense is this? He touches nothing, sees nothing; it can only be by the adjustment of the muscles that the limbs are stiffened, the body firmly balanced and kept erect. In truth, we stand by so fine an exercise of this power, and the muscles, from habit, are directed with so much precision and with an effort so slight, that we do not know how we stand." Such is what is meant by the muscular sense. The Germans, very appropriately call it the "Gemein-gefühl," MUSCLE AND ITS PROPERTIES. 195 the general or common feeling of the body. The vigor of this sense is a criterion of health; it was the euphora of the ancients, the easy carriage and light weight of the body. The muscular sense is the physical conscience. The individual who has this conscience or consciousness sound, enjoys a luxury in mere existence. LECTURE X. MUSCLE AND ITS PROPERTIES. CONTENTS. Contractility of Muscle-Effects of Muscular Contraction-Degree of Contraction-Change of Form-Agents which Induce ContractionDirect and Indirect Excitation-Thermal Excitation-Electric Excitation-The History of Galvanism-The Action of Induced Electricity -The Action of Nerve Force-The Sound of Muscle ContractionThe Muscular Wave-Independence of Muscular Force-The Action of the Sulphocyanide of Potassium and Curare-The Generation of Heat-The Generation of Electricity-Du Bois-Reymond's Theory of Muscular Action-Rigor Mortis-Post-Mortem Changes in Muscle -The Fuel of Muscle-The Oxygen Supply-The Dependence of Muscle upon Blood-The Muscles as Levers-The Absolute Power of Muscle-The Power of Muscle in General-Differences of the Sexes-Differences in Different Animals-The Velocity and Delicacy of Muscular Action. We have to-day to conclude the study of muscle with the consideration of its remaining properties, the chief of which is Contractility. We observe then, first, that the mode of contraction is very different in the two kinds of muscular tissue. Striated muscle responds to an irritant almost suddenly, always forcibly, and as quickly returns to its former state. Smooth muscle responds slowly, always comparatively feebly, and as slowly returns to its former state. The slow, undulatory, 196 THE CONTRACTILITY OF MUSCLE. so-called peristaltic, action of the smooth muscle of the intestinal walls, manifest upon laying open the abdominal cavity of an animal, best exhibits the mode of contraction of smooth muscle fibre. The intestines, at first motionless, soon exhibit feeble contraction, which gradually increases to vermicular motion, until the whole canal "writhes like a mass of earth worms," to gradually become again quiescent. The uterus in labor typically exemplifies the action of involuntary muscle. If the hand be placed upon the abdomen at the commencement of a pain, the uterus is felt to "gather up" its fibres, to become gradually indurated, and then slowly to relax to the condition in the intervals between pains. The character of the pain itself, a gradual increment to an acme, and then a gradual decrement to more or less complete relief, exhibits the absence of any sudden force. But there is a difference in the quickness or sluggishness of response in different involuntary muscles. Thus the muscles within the eyeball, i. e., the muscles of the iris and the tensors of the choroid (muscles of accommodation), respond very nearly as promptly as voluntary muscles; next in order of promptness rank the muscular walls of the intestines and ureters, and slowest of all, is that of the blood vessels, especially of the arteries, which, however, compensate for it in some degree by the long persistence of contraction. Legros and Onimus concluded from their observations, that smooth muscle was influenced more by direct excitation of its substance than by excitation of the nerves, and that the disuse, which would reduce striped muscle to an inactive mass of fat, had little or no effect upon the anatomical or physiological integrity of smooth muscle. The voluntary muscle fibres reach the bones only by the intervention of membranes and tendons. Each fibre is THE EFFECT OF MUSCULAR CONTRACTION. 197 reduced at its end to a point, with flat, facetted, sides, like a diamond or a sharpened lead-pencil, and is thus embraced by the connective tissue structure of the tendon. is the conductor of force. It plays the part which connects the horse to the canal-boat. Effect of Muscular Contraction. The tendon of the line Shortening is only another name for contraction. In contracting, muscle shortens, and, in the case of long muscles, approximates the connected bones. Muscles in the form of tubes (canals, vessels, etc.) diminish, in shortening, the caliber of the tube or obliterate it altogether. It is the spasmodic contraction of the cerebral vessels, which induces the profound anæmia of the brain and pallor of the face as the immediate cause of epilepsy. And it is this exercise of contractility in lesser degree which regulates the blood supply to individual organs independently of the action of the heart. The blood vessels become, thus, local hearts, at the portals, and in the substance, of each organ and structure to increase or diminish the supply of blood according to the demand. Something of this local increase and decrease is observable in the face under the action of the emotions. The face is suffused with blood under the excitement of modesty or shame and is blanched under anxiety or fear. Thus, Donne says: "The eloquent blood Spoke in her cheeks, and so distinctly wrought, And Petrarch descants upon "Quel vago impallidir." (That charming pallor.) A vaulted muscle has its arch reduced by contraction, brought nearer to a plane surface, and thus, in the case of the diaphragm, is the vertical capacity of the chest increased 198 THE DEGREE OF CONTRACTION. and inspiration effected. Ring muscles, like the sphincters and orbiculars, in contracting, "purse up" their respective orifices, and hollow muscles obliterate their cavities to entirely empty themselves of contents. Degree of Contraction. But it is only in extreme cases of cramp, as in tetanus, or in extraordinary effort, that a muscle attains its utmost degree of contraction. The bones very greatly limit the contraction of the long muscles. Thus the biceps will contract, when detached, nearly five-sixths of its length, but, attached, its shortening is limited to but one to twosixths. In tetanus it may reach three-fifths. Strange to say, it is no matter how much muscles vary in size or bulk, the per cent. shortening remains about the same. Some muscles (the glutei) weigh pounds, or measure feet in length (the sartorii), and others, the muscles of the middle ear, but a few grains, and measure but a few lines, but the proportionate shortening remains about the same. Change of Form. The loss which a contracted muscle has experienced in length is in very nearly exact correspondence to its gain in breadth. We may feel the muscles (biceps) in action swell. It was formerly believed that muscle absolutely gained in bulk, but the ingenious experiments of the older physiologists entirely disproved this belief. Thus Sir Gilbert Blane inserted a glass tube into the perforated cork of a glass jar and filled the jar with water up to a certain level in the tube. He now introduced a living eel into the jar and irritated it by means of a stick, also inserted through the cork, to active contractions. Though the slightest increase in the bulk of the animal would have been registered in the tube by an elevation in the column of water, no such change in |