Part 7

VI. Phenomena of the Relaxation of the Organic Muscles.

In the relaxation of the organic muscles, phenomena in general take place that are opposite to the preceding. It is then useless to enumerate them; but there is a question here that should be examined, that of knowing the nature of that state which succeeds contraction and alternates with it.

In the muscles of animal life, when the contraction ceases, the muscle does not in general go back itself to the state it was in antecedent to the contraction, but it is drawn back to it by its antagonist; for example, when the biceps is contracted to bend the fore-arm and its contraction ceases, it becomes passive; the triceps putting itself then in motion, extends it and draws it back to its natural position, by acting at first on the bones which communicate the motion to this muscle. Each muscular power of animal life finds then in that which is opposed to it a cause of return to the state it had left in order to contract. It is not so in organic life; its muscles, which are all hollow, have no antagonists. We have considered as such to a certain extent, the substances contained in the hollow muscles, substances which oppose the effect of contraction; but incapable most commonly of reacting after having been compressed, on account of their want of elasticity, these substances cannot perform the same offices as real antagonists.

Most physiologists have admitted as a cause of dilatation, the entrance of new substances, which replace, in the muscular cavities, those expelled by contraction; thus the entrance of new blood into the heart, aliments into the different portions of the alimentary canal, has been considered as proper to dilate these organs; so that according to this opinion the muscles would be purely passive when they enlarged. But the following considerations, many of which some authors, Grimaud in particular, have already stated, do not permit us to consider in this way the dilatation of the organic muscles, that of the heart in particular.

1st. When we lay bare a hollow muscle, the heart, the stomach, or the intestines, and empty it entirely of the substances that it contains, it contracts and dilates alternately as when it is full, if we apply an external stimulant to it. 2d. If we empty by punctures all the great vessels which go to the heart, or come from it, so as to evacuate it entirely, its alternate dilatations and contractions continue for some time. 3d. In order to judge comparatively of the degree of force of the contraction and the dilatation, we can extract two hearts nearly equal in size from two living animals; place immediately the fingers of one hand into the auricles or the ventricles of the first, and grasp with the other hand the exterior of the second; you will feel that one makes as great an effort in dilating as the other does in contracting. This fact already observed by Pechlin, is so much the more remarkable, as the effort of dilatation is often greater than that of contraction. I have even observed, in repeating this experiment, that whatever effort we make with the hand, we cannot prevent the organ from dilating. 4th. The alternate extension and contraction, from which arises the vermicular motion of the intestines, is seen during hunger when we open the abdomen of an animal. 5th. The hardness of the organic muscular texture is as evident during dilatation as during vacuity. 6th. I have many times observed that at the instant in which I irritated the heart with the point of a scalpel, that a dilatation was the first consequence of it, and that contraction was only consequent to it. It happens in general more often that contraction begins the motions in our experiments; but certainly, the muscle being at rest, it is frequently a dilatation that first manifests itself.

It appears then very probable that the dilatation of the organic muscles is a phenomenon as vital as their contraction; that these two states are united in a necessary manner; that both of them compose muscular motion, of which contraction is but one part. Who knows even if each may not be disturbed separately, if to a regular contraction may not succeed an irregular dilatation and vice versa? Who knows if certain alterations in the pulse do not belong to injuries of dilatation and others to those of contraction? I am far from being certain; for in medicine we must rest our belief on certainty and not on presumption; but we can make this point an object of research.

It appears that sometimes the voluntary muscles are also the seat of a true active dilatation. 1st. A muscle, laid bare and extracted from the body, contracts and afterwards dilates, without being drawn to this state of dilatation by any cause. 2d. In an amputation, we often see in the stump the end of the divided fibres alternately lengthen and contract; a double motion both of which appears to be equally vital. 3d. In many kinds of convulsions in which the extremities stiffen, in those, for example, which accompany most hysterical fits, it appears that there is a very evident active dilatation; by placing in fact the hand upon the muscles which should then be relaxed, from the disposition of the parts, we perceive a hardness as great as in feeling of the contracted muscles.

There are many researches to be made upon this mode of dilatation of our parts, a mode which undoubtedly is not exclusively confined to the muscular system, but which appears to belong also to the iris, to the spongy texture of the corpora cavernosa, to the nipples, &c. All these organs move by dilating very evidently; contraction succeeds in them expansion, as in the common muscles relaxation does contraction. Expansion is the principal phenomenon. Perhaps also, as some modern authors have thought, the sudden swellings of the cellular texture, which accompany contusions, bruises, &c. are the result of this mode of motion.

ARTICLE FIFTH.

DEVELOPMENT OF THE MUSCULAR SYSTEM OF ORGANIC LIFE.

The organic muscular system is wholly the reverse of the preceding, as it respects development. This is but slightly characterized in the early ages, whereas the growth of the other is precocious. Let us follow it in all the ages.

I. State of the Organic Muscular System in the Fœtus.

In the first days after conception, the heart is formed; it is the first point of motion, a punctum saliens, as it has been called. The researches of different authors, of Haller in particular, have rendered clear the successive progress of its increase in the early periods. Rather late in their formation, the muscles of the interior of the abdomen are yet developed before those that form the parietes of this cavity. It is the size of the intestines, the stomach, the bladder, &c. almost as much as that of the liver, which gives to the cavity in which these viscera are found, the remarkable capacity that it then exhibits.

Nearly uniform at this age, as it respects the proportion of their size, all the organic muscles are not as much so in regard to that of their texture. The heart is evidently firmer and more dense than all the others; its texture is very distinct. The fibres of the stomach, intestines and bladder are soft and loose and resemble exactly those of the muscles of animal life; but little blood goes to them in proportion to what they are afterwards to receive. The fibres of the heart, on the contrary, dense and compact, have a power of action in proportion to what they are afterwards to have. Their redness is as distinct; as much blood penetrates and consequently nourishes them. This redness of the heart, analogous in the adult to that of the voluntary muscles, forms at this period a contrast with the remarkable paleness of these muscles. Besides it has, as in all the other parts where it exists, a deep tinge, owing to the kind of blood that produces it.

We easily see the reason of the quantity of blood that penetrates the heart, as this organ then very active in its motions, has need of much force, whilst the others, almost immoveable, require but little.

Yet the sensible organic contractility of the heart in the fœtus and in the first age has been exaggerated, undoubtedly on account of the extreme rapidity that the circulation then exhibits. This rapidity depends as much on the activity of the tonic forces of the general capillary system, as on that of the heart; for the blood, when it has arrived in the capillary system, is wholly beyond the influence of the heart, as we have seen; the stay that it makes there is wholly dependant upon the forces of the system itself; now these forces, at that time very active, accelerate the course of the blood, and send it into the venous system, from which it goes to the heart. If the excitability of this were double and even treble, and the blood entered it but slowly, it would be unable to support a rapid and at the same time continuous pulse. Haller was drawn to this opinion by believing that the heart was the only agent of impulse of the blood circulating even in the small vessels. Besides, there is no doubt that the sensible organic contractility of the heart is less easily put into action by experiments in the fœtus, and that it is also much less durable. Then the strongest stimuli have less effect upon it an instant after death, than those of less power exhibit upon the heart of an animal that has been born. I have many times established this fact upon fœtuses of guinea-pigs. Compared with that of the voluntary muscles, the mobility of the heart is undoubtedly remarkable in the fœtus; but compared to what it will be after birth, it is but slight.

It is precisely the same with the contractility of the stomach, the bladder and the intestines; most commonly we can produce no motion in these muscles by stimuli. Mr. Léveillé has already made these important observations; he has also remarked that the urine remained in the bladder, and the meconium in the great intestines, without producing a contraction sufficient to expel them. I do not think however that there could be during life a complete immobility of the gastric viscera, and for this reason; most commonly the meconium is only met with in the great intestines; it must have been formed in them then, if there was complete immobility of the gastric muscles; now it is much more probable that it is the residuum of the bile, of all the mucous juices, &c.; that consequently it has been pushed successively by a slow action from the superior part towards the inferior of the alimentary canal.

The softness of the organic muscles renders their extensibility of texture very great at this period. I would observe however that the hearts of dead fœtuses do not exhibit those numberless varieties of size which those of adults do in the right side, according to the different kinds of death.

II. State of the Organic Muscular System during Growth.

The first days of existence are marked by an internal motion as quick in manifesting itself as the external of which we have spoken. The sucking of the milk, the evacuation of the urine and meconium, &c. are indices of this general internal motion, of this agitation almost sudden of all the involuntary muscles.

It is not the brain which, entering into action at birth, produces the contraction of these muscles, since as we have said they are not under its government; it appears to depend, 1st, on the sympathetic influence exerted upon their system, by the cutaneous organ, which is irritated by the new medium; 2d, on the excitement made upon the beginning of all the mucous surfaces, and upon the whole of that of the lungs, an excitement which afterwards reacts upon these muscles; 3d, on that produced by fluids introduced into the stomach; 4th, on the sudden entrance of the red blood into all these muscles, till then penetrated like the others with black; this cause is essential; irritability appears to be in part dependant on it, or at least to borrow from it a remarkable increase of force; 5th, the excretion of the meconium and the urine is also powerfully assisted by the abdominal muscles, which then enter into activity with the whole system to which they belong.

The general internal motion which takes place in the first moments of existence, and which is produced by the suddenly increased activity of the involuntary muscles, has an important use with respect to the mucous surfaces, which it relieves of the fluids that load them, and whose presence becomes painful. Where the mucous surfaces have not around them fleshy layers of the involuntary muscles, as in the bronchia, the nasal fossæ, &c. the muscles of animal life more or less distant, perform this function, as for example, the diaphragm and the intercostals, free the bronchial surface by coughing, and the pituitary by sneezing.

As we recede from the period of birth, the organic muscles grow in general much less in proportion than the others; it is this that gradually re-establishes the equilibrium between the two systems. I would remark however, as it respects the predominance of the first, that it is much less conspicuous in the fœtus than that of the nervous system. The brain, for example, is in proportion much larger than the heart.

It is probable that the muscles of which we are treating, exhibit, at this period, the same varieties of composition as the others, that gelatine especially predominates in them, that they have less fibrin, &c. This last substance perhaps exists, in the early periods, more abundantly in the heart than in the other muscles of this class.

We have observed two very distinct periods in the growth of the other muscles; one is finished when they have acquired their length; the other, when their thickness is complete. The first has not, in the organic system, a term as distinct; when the stature no longer increases, the gastric and urinary organs, and the heart still lengthen and grow.

We have considered growth in too general a manner. Each system has a different term in this great phenomenon. The osseous and muscular systems of animal life, and those which depend on them, as the fibrous, the cartilaginous, &c. have especially an influence upon the general stature of the body; it is these which produce this or that height; but this height has no influence upon the length of the intestines, or the capacity of the stomach, the heart, the bladder, &c. The glandular, serous, mucous systems, &c. are equally independent of stature; thus in these numerous varieties, it has much more influence upon the extremities, than upon the abdomen, the thorax, &c. A great height indicates the predominance of the apparatus of locomotion, but not of those of digestion, respiration, &c. The termination of the growth in height, which we consider in a general manner for the whole body, is only the termination of the growth of the muscles, the bones and their dependancies, and not of that of the internal viscera, which still lengthen and become thicker. It is easy to be convinced of this, by comparing the organic muscles of a young man of eighteen years, with those of a man of thirty or forty.

The organic muscles do not appear to be subject to those irregularities of growth which the other muscles and the bones frequently exhibit. We know that the stature often remains stationary for many years, and that suddenly it acquires very great dimensions in a very short time; this phenomenon is remarkable especially after long diseases. Now notwithstanding these inequalities, the heart and all the other analogous muscles grow in an uniform manner; the regularity of the internal functions to which these muscles especially contribute, could not adapt itself to those aberrations which would be unable to disturb the functions of the locomotive organs. Besides, if they took place, the circulation, digestion, excretion of urine, &c. would exhibit corresponding aberrations; now this is never observed. The heart and the gastric muscles, &c. always grow in an infant whose stature remains stationary; they do not grow suddenly in one who grows at once; hence why the thorax and the abdomen become large in the first case, and remain contracted in the second in proportion to the extremities.

Besides these two systems are never in precise relation of nutrition and power. I have already observed that very large organic muscles often exist with very small voluntary ones, and vice versa.