Part 5

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.

Let us consider neither the growth nor nutrition in an uniform manner; each system is developed and increases in its own way; all are never found at the same periods of this function. Why? because nutrition, like all the other acts over which life presides, is essentially dependant on the vital forces, and these forces vary in each system.

The growth of the involuntary muscular system is not uniform in all the organs which compose it. Each increases more or less, or is differently developed; one often predominates over the others in an evident manner; a bladder with strong, fleshy fibres, with columns as they are called, is often found in a subject with a debilitated stomach, with small intestines, &c.; reciprocally, the stomach, the heart, &c. have often an insulated predominance.

III. _State of the Organic Muscular System after Growth._

It is from the twenty-fourth to the twenty-sixth year, that the organic muscles are completely developed. Then the thorax and the abdomen which contain them have their greatest capacity. These muscles are then as they are to remain through life; they have a density much greater than in youth; their power is increased and their colour is deeper. In general this is subject in the heart to frequent varieties, which coincide very nearly with the varieties of the preceding system. Acute and chronic diseases have nearly the same influence upon it. It is equally the index of the sanguineous, lymphatic temperaments, &c. by the different tinge it assumes. The colour of the gastric, intestinal and vesical fibres varies less; their whiteness, more uniform, is rarely influenced by diseases.

We cannot increase, by constant exercise, the nutrition of the organic muscles. Aliments taken beyond measure, making the stomach frequently contract, weaken it instead of developing its fibres more, as happens from constant exercise given to a superior or inferior extremity. The bladder incessantly in action in some cases of incontinence, is thus gradually weakened and loses its energy. We might say that these two systems were in this respect in an inverse order.

It appears that the nutrition of the organic muscles, like that of the others, is subject to frequent variations; that at some periods they are more developed and less so at others. Diseases have a great influence upon this phenomenon, which proves, like the softening of the bones and their return to the natural state, the constant composition and decomposition of which these organs are the seat. We find in the dissecting rooms many differences in different subjects, as it respects the colour, density and cohesion of the muscles. Now what many exhibit then at once, the same individual often experiences successively; the same man no doubt has, according to the different influences to which he is exposed, his heart red, dense, large and well nourished at one period of life, and feeble, pale and small at another; for the internal organs experience the same alterations as the exterior. Now we know that the external appearance often changes during life.

IV. _State of the Organic Muscular System in Old Age._

As we advance in age, the muscular system of which we are treating becomes weak like all the others; yet its action is more durable; it survives, if we may so say, that of the other. When the old man, almost immoveable, crawls about but slowly and with pain, his pulse, digestion, &c. have vigour still. This difference of the two systems is so much the more remarkable, as the time of activity of the second is almost by half less than that of the first; sleep cuts off in fact almost half of the duration of the voluntary motions, whilst it leaves the involuntary wholly untouched. This phenomenon of the organic muscles as it were surviving the voluntary in the last periods of life, is derived on a great scale from the same principle from which arises on a small one the lassitude which follows the contraction in an insulated motion. A less durable motion is necessary to fatigue the voluntary muscles, than to fatigue the involuntary; the stomach empty remains for a long time contracted upon itself without producing any painful sensation, whilst if we hold a body strongly grasped between our fingers for a quarter of an hour, all the flexors are soon painfully affected. After a convulsion of half an hour, in which all the locomotive muscles have been stiff, the whole body is broken, as it is called; it cannot admit of any motion; whilst after a paroxysm of fever of six or eight hours in which the pulse has been violently agitated, the heart often preserves the natural type of its contractions; it requires repeated paroxysms to weaken it. All these phenomena of the two muscular systems evidently prove that that of animal life is fatigued much the soonest; it is this which occasions its intermission. Is it then astonishing that, although less often in exercise than the other, it exhausts sooner the quantum of force nature has given to it? is it astonishing that the other survives the longest? Life is a great exercise which gradually wears up the organs in motion, and which requires their rest; this rest is death; now each moveable organ arrives at it sooner or later, according to the different degree of the forces which it has to expend, and according to its greater or less disposition to be wearied by this great exercise.

Yet the organic muscles are gradually weakened. The pulse becomes slower, digestion is longer in old age; the bladder and rectum first cease to act; then the intestines remain inactive; the stomach and especially the heart die the last.

A long time before death, the muscular cohesion is weakened in this system as in the preceding; the fleshy texture becomes flaccid; the parietes of the heart support themselves in youth; they flatten in old age. The gastric system of a young animal suddenly killed during hunger is firm, dense and contracted upon itself; in an old one, under the same circumstance, it is but little contracted; the stomach and intestines remain much more dilated; they are loose and soft; it is the same phenomenon as in the preceding muscles, which vacillate under the skin, from want of cohesion. The bladder remains constantly large, though empty.

MUCOUS SYSTEM.

This system, the name of which I borrow from the fluid that constantly lubricates it, and which is furnished by small glands inherent in its structure, appears everywhere in a membranous form; that of fasciculi is wholly foreign to it. In speaking of the mucous organs we shall designate them almost always under the name of membranes. Their study is a new object of research. Pinel has been among the first, who has perceived the necessity of considering them in a general manner as it respects diseases. I believe that I am the first who has regarded them generally in an anatomical and physiological view. Few systems deserve more attention; upon it take place all the great phenomena of digestion, respiration, secretion, excretion, &c.; it is the seat of many diseases. It should alone, in a nosography in which diseases are distributed by systems, occupy a place equal to that of many.

ARTICLE FIRST.

OF THE DIVISIONS AND FORMS OF THE MUCOUS SYSTEM.