and of the fibrine of the blood cannot be altogether without relation to the mystery of muscular action, and it is necessary that the deductions which have arisen during their consideration be borne in mind in the inquiries upon which we now enter. I. OF MOVEMENTS SUCH AS ARE SEEN IN THE Now "Wherever the striated structure occurs, we witness an aptitude for quick, energetic, and rapidly repeated movements; while, where it is deficient, they are sluggish, progressive, and more sustained." the non-striated muscles, which belong to the system of organic life, are much more sparingly supplied with nerves and blood vessels than the striated muscles of the voluntary system; and as the phenomenon of contraction is most conspicuous in the variety most sparingly supplied with nerves and vessels, it would seem to be a legitimate inference that the nervous and vascular influence, be this what it may, is intended to counteract, rather than to induce, contraction. let us examine the subject in detail. But 1. Of intra-organic force as the agent in these movements. (a.) Of the nervous influence as an agent. In a state of fear, when the blanched skin, the faltering heart, and the occurrence of fainting, show how greatly the supply of nervous force has been repressed, the condition of the organic muscles is one of contraction. The pallor of the countenance and the smallness of the pulse is a sufficient proof that this is the case in the fibrous tissues which enter into the walls of the vessels. In parts, also, where the muscular fibre is more developed, as in the coats of the several visceral cavities, the result is the same; and thus, during the continuance of fear, there is a tendency to contract and expel their contents-a fact which is equally apparent in the alimentary canal, in the bladder, and in the uterus. In the first instance, it may be supposed that fear operates by inducing a state of paralysis in a sphincter muscle; but in the bladder and uterus no doubt of this nature can exist, inasmuch as the openings of these organs are destitute of sphincter fibres. Moreover, in the case of the alimentary canal, it must be observed that the tendency to evacuation, under the operation of fear, involves a powerful and sudden contraction of the coats; for the mere paralysis of the outlet, which is itself supposititious, is not sufficient to account for the results. In maniacal frenzy, on the other hand, where there is a superabundant generation of nervous force, the results would seem to be entirely opposed to those which have just been considered. The hot and reddened skin, and the full pulse, necessitate, indeed, a distended state in the fibrous elements of the vascular coats; and the obstinate constipation of the bowels, and the retention of urine, which are such frequent symptoms of this condition, are facts which argue the existence of a state opposed to contraction in the walls of the viscera concerned. (b.) Of the organic forces, not of a nervous character, as agents in the movements under consideration. The influence of the blood upon the coats of the small vessels, and consequently upon the muscular fibres contained in these coats, has been considered in the last chapter; and it has been seen that this influence, whatever it may be, does not give rise to contraction. Wherever the blood possessed peculiarly stimulating properties, whether in consequence of a formation from rich pabulum, or as the result of perfect oxygenation, on these occasions the vessels are freely distended; and, on the contrary, whenever the blood is pale and watery, and the respiration faulty, then the vessels are shrunken and collapsed. In so far, therefore, as concerns the muscular tissue present in the coats of these vessels, it is evident that the state of contraction is not induced by the stimuJant properties of the blood. In nature and office the blood vessel is very intimately related to the alimentary canal; and hence it may be expected that the influence of the food and the blood, upon the passages with which they are severally related, will present many points of correspondence and analogy. And such indeed is the fact. The food is said to stimulate contraction in the coats of the alimentary canal; but let us examine what is involved in this supposition. If a morsel acts in this manner, how is it, we may ask, that the act of contraction does not prevent its admission into the gullet; or if by chance it be admitted, how is it that it is not immovably fixed there? There is no physical necessity that the muscular acts should follow in a certain and definite order; for, in the ordinary peristaltic movements, an impulse which passed in one direction at first may the next moment be entirely reversed. Again; in the movements of the gullet in the cow, or in any other ruminant animal, we have a simple proof of this fact; for, during the process of rumination, the morsel is seen to ascend and descend alternately, where the gullet lies superficially at the side of the neck. There is no reason, therefore, so F far as we may perceive, why the food should pass in one direction rather than another, or why the act of contraction, which is supposed to be excited by the food, should, in the natural course of things, be behind, and not before the morsel. The entire history of the assimilative function, however, is at variance with the idea that the food induces contraction in the alimentary canal: indeed the constant lesson is that the food remains within the digestive apparatus so long as any molecular changes are unaccomplished, and that expulsion takes place, and the effete matter is expelled, only when these changes are at an end. The ingestion of food into the stomach does not cause this organ to contract, nor does any contraction interrupt the process of digestion; and it is only when the gastric juices have effected their office and the food is dissolved, that the contraction takes place, by which the food is transposed to the duodenum. In the small intestines, the food remains during the continuance of the processes of ulterior digestion, and it is transmitted onwards, only when these are at an end And lastly, there is no contraction in the large intestines, until the digestive changes are completed. So long, therefore, as there are any evidences of the continuance of molecular changes, by which the food could act as a stimulus to the muscles of the alimentary canal, so |