Chapter III: Part 3

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.

The mucous membranes occupy the interior of the cavities which communicate with the skin by the different openings this covering has on the surface of the body. Their number at first view is very considerable; for the organs in which they are reflected are very numerous. The mouth, the stomach, the intestines, the œsophagus, the bladder, the urethra, the womb, the ureters, all the excretories, &c. &c. derive from these membranes a part of their structure. Yet if we consider that wherever they are continuous, wherever we see them originate, by extending from each other, as they originated in the first instance from the skin, we shall perceive that this number must be wonderfully limited. In fact by thus describing them, not separately in each part, but at the same time in all those upon which they are continued, we see that they are reduced to two general surfaces, of which all the others are portions, and which, on account of the different parts to which they are distributed, can be called, the one gastro-pulmonary, the other genito-urinary. The first is found in the head, the neck and the abdomen. This last cavity and more especially the pelvis, contain the second.

There is also a small insulated mucous surface; it is that which enters by the openings of the nipples and lines the lactiferous tubes. But it is so small that it deserves but little attention; besides, what will be said of the two others will be equally applicable to it. It is then useless to examine it in a general manner.

I. _Of the two General Mucous Membranes, the Gastro-Pulmonary and the Genito-Urinary._

The gastro-pulmonary surface penetrates into the interior by the mouth, the nose and the anterior face of the eye. 1st. It lines the first and second of these cavities, extends from the first to the excretory ducts of the parotid and sub-maxillary glands, from the other into all the sinuses, forms the conjunctiva, dips down into the puncta lachrymalia, the nasal duct, the sac of the same name, and is continued into the nose; 2d, it descends into the pharynx, furnishes an elongation to the Eustachian tube, then penetrates the internal ear and lines it, as we shall see; 3d, it dips down into the trachea and is spread upon all the air-tubes; 4th, it penetrates into the œsophagus and the stomach; 5th, it extends to the duodenum where it furnishes two elongations, one destined to the ductus choledochus, to the numerous branches of the hepatic and cystic ducts and the gall-bladder, the other to the pancreatic duct and its different branches; 6th, it is continued into the small and large intestines and finally terminates at the anus where we see it identified with the skin.

The second general mucous membrane, which we have called the genito-urinary, enters in man by the urethra, and thence is spread on the one hand upon the bladder, the ureters, the pelvis of the kidnies, the infundibula, the papillæ and the capillary tubes which open on their summit; on the other hand it goes into the excretory tubes of the prostate, into the seminal ducts, the vesiculæ seminales, the vasa deferentia and the branches with numberless windings that produce them.

In woman, this membrane is introduced by the os externum and penetrating on the one hand by the urethra, goes as in man upon the urinary organs; on the other hand, we see it enter the vagina, lining it, the uterus and the fallopian tubes, and afterwards becoming continuous with the peritoneum by the opening of these tubes. It is the only example in the economy, of a communication established between the mucous and serous surfaces.

This manner of describing the course of the mucous surfaces, by saying that they are elongated, dip down, penetrate, &c. from one cavity to another, is no doubt not conformable to the progress of nature, which creates in each organ the membranes belonging to this organ, and does not thus extend them by degrees; but our manner of understanding it is better adapted to this language, the meaning of which the least reflection will show.

In thus referring to two general membranes all the mucous surfaces, I am not only supported by anatomical inspection, but pathological observation has also furnished me with points of demarcation between the two, and points of contact between the different portions of membranes of which each is the assemblage. In the different descriptions of catarrhal epidemics given by authors, we frequently see one of these membranes affected in all parts, the other remaining sound; it is especially not rare to observe a general affection of the first, of that which extends from the mouth, the nose, the surface of the eye, into the alimentary canal and the bronchial vessels. The last epidemic observed at Paris, with which Pinal himself was affected, was of this character; that of 1761, described by Razou, had it also; that of 1752, described in the memoirs of the Society of Edinburgh was remarkable for a similar phenomenon; now, we do not see at that time a corresponding affection in the mucous membrane that is spread upon the urinary organs and upon those of generation. There is then here, 1st, an analogy between the portions of the first, by the uniformity of affection; 2d, a demarcation between the two by the health of the one and the disease of the other.

We see also that the irritation of any one point of one of these membranes, frequently produces a pain in another point of the same membrane, which is not irritated. Thus a calculus in the bladder occasions a pain at the end of the glans penis, the presence of worms in the intestines causes an itching of the nose, &c. &c. Now, in these phenomena purely sympathetic, it is very rare that the partial irritation of one of these two membranes affects with pain one of the parts of the other; there are however examples of it; such is the singular relation that exists, in mucous hemorrhages, between the membrane of the womb and that of the bronchia. If the blood ceases accidentally to flow from one during menstruation, the other frequently exhales it and thus as it were supplies its functions.

We ought then, from inspection and observation, to consider the mucous surface, in general, as formed by two great membranes successively spread upon many organs, having between them no communication except by the skin, which serves them as an intermediate organ, and which, continuing with both, contributes thus with them to form a general membrane everywhere, continuous, covering the animal externally, and extending within upon most of its essential parts. We can conceive that there should exist important relations between the internal and external portion of this single membrane; and that they do will be proved by further researches.

II. _Adhering Surface of the Mucous Membranes._

Every mucous membrane exhibits two surfaces, one adhering to the neighbouring organs, the other free, covered with villi, always moistened with a mucous fluid. Each deserves particular attention.

The adhering surface corresponds almost everywhere with the muscles, either of animal or organic life. The mouth, the pharynx, the whole alimentary canal, the bladder, the vagina, the womb, a portion of the urethra, &c. exhibit a muscular layer embracing on the outside their mucous tunic which is within. This arrangement coincides perfectly, in animals with a fleshy membrane, with that of the skin, which moreover approximates very near, as we shall see, the structure of the mucous membranes, and which, as we have seen, is everywhere continuous with them. This arrangement of the mucous membranes occasions them to be agitated by constant motions which favour wonderfully the secretion that takes place in them, the excretion which succeeds it, and the various other functions of which they are the seat. The insertion of this muscular layer exterior to the mucous system, is made, as we have seen, by this dense and compact texture which I have called the sub-mucous. It is from this texture, more compact than the rest of the cellular system, that the mucous surface derives its force. It is from it that the organ which it lines receives its form; it is this which supports and preserves this form; the following experiment proves it. Take a portion of the intestine; remove from any part of it this layer, as well as the serous and the muscular; then inflate it, after having tied it below; the air produces in this place a hernia of the mucous coat. Try afterwards another portion of intestine; deprive this, for a small space, of its mucous membrane and of this also; inflation will produce upon the serous and muscular tunics the same phenomenon that it did in the preceding on the mucous; then it is to this sub-mucous cellular layer that it owes the resistance with which it opposes substances that it contains. The same may be said of the stomach, the bladder, the œsophagus, &c.

III. _Free Surface of the Mucous Membranes._

The free surface of the mucous membranes, that which is continually moistened by the fluid from which they borrow their name, exhibits three species of wrinkles or folds.

1st. One inherent in the structure of all the laminæ of these membranes, is constantly met with, whatever may be their state of dilatation or contraction; such are those of the pylorus and the valve of Bauhin. These folds are formed not only by the mucous membrane, but also by the intermediate tunic of which we have spoken, which here has a remarkable density and thickness, and gives them solidity. The fleshy tunic enters even into their composition, and we see on the exterior, upon the serous surface, a depression that indicates their presence.

2d. Other folds, only formed by the mucous surface, exist also always in a state of vacuity or fulness, less evident however than this; they are owing to the circumstance that the mucous surface is much more extensive than those upon which it is applied, so that it is folded that it may not run a longer course; such are the valvulæ conniventes of the small intestines, the structure of which we see very well by cutting longitudinally one of these intestines. The edge of the section exhibits the fleshy layer and the serous surface in a straight direction, whilst the mucous layer describes a line resembling a loose thread.

3d. The last species of folds is as it were accidental, and is only observed during the contraction of the organ which is lined by the mucous surface that is the seat of it; such are those of the interior of the stomach, the great intestines, &c. In the greatest number of subjects brought to the dissecting rooms, these folds of which so much has been said as it respects the stomach, cannot be perceived in it, because the subject has died after a disease that has so altered the vital forces, as to prevent all action of this viscus; so that though it is frequently found empty, its fibres are not contracted. In experiments upon living animals, on the contrary, these folds become very evident, and may be demonstrated in this way; make a dog eat or drink copiously, open him an instant after and cut the stomach in the length of its great curvature; no fold is then apparent; but soon the viscus contracts, its edges are turned over and the aliments escape; the whole mucous surface is covered with an infinite number of very prominent ridges, which have as it were the form of cerebral circumvolutions. We obtain the same result by taking out the stomach of an animal recently killed, distending it with air and opening it afterwards, or by cutting it immediately in its state of vacuity and drawing it in opposite directions by its edges; it stretches, its ridges disappear, and if we cease to distend it, they form again immediately in an evident manner. I would observe on the subject of the inflation of the stomach, that by distending it with oxygen, we do not produce by the contact of this gas, greater ridges and consequently a stronger contraction, than by using for the same purpose carbonic acid gas. This experiment furnishes a result very similar to what I have observed in rendering animals emphysematous by different aeriform fluids. It follows from all that we have said upon the folds of the mucous membranes, that in the ordinary contraction of the hollow organs which these membranes line they undergo but a very slight diminution of surface, that they contract scarcely at all, but fold within, so that by dissecting them on an organ in contraction we should have a surface almost equal in extent to that which they exhibit during its dilatation. This assertion, which is true as it respects the stomach, the œsophagus and the great intestines, is not perhaps as entirely so with regard to the bladder, the contraction of which makes the ridges within less evident; but they are not sufficient to destroy the general law. It is also nearly the same with the gall-bladder; yet here we find another cause. The gall-bladder, alternately observed in hunger and during digestion, contains double the bile in the first case that it does in the second, as I have had occasion to see very often indeed, in experiments made for this object or with other views. Now, when the bladder is in part empty, it does not contract upon the bile that remains, with the force of the stomach when it contains but few aliments, or with the power of the bladder when it contains but little urine. It is then flaccid; so that its being distended or not has but a slight influence upon the folds of its mucous membrane.

Besides, in saying that the mucous membranes always exhibit, with some slight difference, the same surface in the extension and contraction of their respective organs, I intend to speak only of the ordinary state of the functions, and not of those enormous dilatations of which we often see the stomach, the bladder, and more rarely the intestines become the seat. Then there is no doubt, a real extension and contraction, which coincide in the membrane with those of the organ.

A remarkable observation which the free surface of the mucous membranes exhibits, and which I have already pointed out, is, that this surface is everywhere in contact with bodies heterogenous to that of the animal, whether these bodies introduced from without to nourish it have not yet been assimilated to its substance, as we see in the alimentary canal and in the wind-pipe; or whether they come from within, as we observe in all the excretory ducts of the glands, which all open into cavities lined by the mucous membranes, and transmit without particles which, after having contributed for some time to the composition of the solids, become heterogeneous to them, and are separated from them by the constant motion of decomposition which takes place in living bodies. Hence we ought to regard the mucous membranes as limits, and barriers, which, placed between our organs and the bodies that are foreign to them, defend them from the mischievous impression of these bodies, and serve consequently within, the same functions which the skin performs without, with respect to the bodies which surround that of the animal, and which tend incessantly to act upon it.

The organization of the mucous system and its vital properties are accommodated to this habitual contact of substances heterogeneous to the living economy. That which is a foreign body to the other systems, the cellular, the muscular, &c. is not so to this. Solid substances, the metals, stones, wood, &c. which introduced into our parts excite in them inevitably suppuration and an antecedent inflammation by their simple contact, pass with impunity over this, provided that their angles and asperities do not tear it; they only augment a little the secretion, as I shall say. We can swallow a ball of lead, of wood, &c. and pass it by the anus without inconvenience. All the irritating fluids without being caustic, that we inject into the great intestines in enemas, or that we swallow, would produce abscesses, &c. if they were forced into the cellular system, &c. Surgeons employ the term foreign bodies in too general a manner; that which is so for one system, is not for another. Foreign is, in this respect, a term of comparison which we should employ only after a knowledge of the peculiar sensibility of each system, and not after that of this property described in a vague manner.

The mucous system not only bears without danger the presence of all bodies that are introduced into the economy, but also when it goes out, it can be exposed with impunity to the contact of external stimuli. Observe what takes place in prolapsus of the womb in which the whole membrane of the vagina sometimes becomes external, in those inversions of the intestinal tubes that take place through preternatural ani, in prolapsus of the rectum, &c.; then the mucous surfaces serve really as integuments; now in these cases the surrounding bodies produce hardly any more pain on them than upon the skin. On the contrary, the instant a serous surface is laid bare, as for example in the operation of hernia, in which the intestine is suffered to come out, on account of an opening unfortunately made by the point of a bistoury, this surface inevitably inflames. All the cellular, muscular, nervous, glandular systems, &c. laid bare, exhibit the same phenomenon. There is no danger in opening the bladder as it respects the contact of the air, whilst there is much in permitting this fluid to penetrate into an articular cavity, a tendinous groove, a serous sac, &c. We know how much in the high operation for the stone, we fear to wound the peritoneum, how uncertain are the results of empyema on account of the contact of the air upon the pleura, &c. The dangers of the action of this fluid upon these surfaces have been perhaps exaggerated, but they are notwithstanding real.

If a fistula extends from the exterior of the abdomen into the intestines, its whole course is lined with callous bodies; these defend the cellular texture and the muscles through which the fistula passes. On the contrary, nothing similar appears upon the intestinal mucous surface, because its organization alone is sufficient to protect it. The urinary, salivary and lacrymal fluids never escape externally by artificial ducts formed in the neighbouring organs, without there are similar callous bodies in the course of these ducts; on the contrary, they pass with impunity over the mucous surfaces. Make in a limb a long and straight opening with a pointed instrument, and fix in it for a time a sound; a callous canal will be produced by it. Let a sound on the contrary remain in the urethra, no alteration of texture will result from it.

Let us conclude from these different considerations, that the mucous system with the cutaneous alone, is organized so as to support the contact of all external bodies, and not to be affected by their presence, or at least experience only an increase of secretion, which is in no ways dangerous. Thus these two systems form two boundaries, the one internal and the other external, between which are placed the organs foreign, by their mode of sensibility and by that of their structure, to the external bodies. To these boundaries the excitement of these bodies is limited; their influence does not go beyond. So long as they do not pass these boundaries, the other organs do not feel them. We might say that the acute sensibility which each of them enjoys, is a kind of sentinel that nature has placed on the confines of the organic domain of the mind, to inform it of whatever can injure it.

ARTICLE SECOND.

ORGANIZATION OF THE MUCOUS SYSTEM.

I. _Texture Peculiar to this Organization._

The mucous system presents two things to be considered in its peculiar texture, viz. 1st, a layer more or less thick which constitutes principally this texture, and which by analogy with the cutaneous corion, may be called the mucous corion; 2d, many small elongations which surmount it, and which are called villi or papillæ. As to the epidermis which covers it, I shall treat of it with the cutaneous epidermis. This texture has nothing similar to the substance that colours the skin, and which is between the papillæ and epidermis. We know in fact that negroes, as well as whites, have this texture of a bright red, which it derives from its vessels.

_Mucous Corion._

This portion of the mucous texture, which is the most important, and which constitutes the thickness, form, and even the nature of it, has a soft and spongy appearance. We might say at first view that it was a consistent pulp, with which the extremely dense cellular texture that is subjacent to it had been covered. This softness is a character which distinguishes it from the cutaneous corion, which moreover has by its intimate nature but little resemblance to it.

The mucous corion is very various as to thickness; it differs in this respect in each organ. That of the gums and the palate is the thickest of all. Then come those of the nasal fossæ and the stomach, then those of the small intestines and the gall-bladder, then those of the large intestines, of the urinary bladder, the urethra and the other excretories, until it begins at length to become so fine as to appear transparent like a serous surface when it is removed with care. Finally, the finest and most delicate is that of the sinuses of the face and the interior of the ear; the arachnoides is often coarser.

I have called the texture within the ear mucous, though all anatomists call the membrane of the cavities of this organ periosteum. In fact, 1st, we see it evidently continued with the pituitary membrane, by means of the elongation of the Eustachian tube. 2d. We find it constantly moistened by a mucous fluid which this canal serves to convey out, a character foreign to the periosteum, which, like the fibrous membranes, always adheres by both its surfaces. 3d. No fibre can be distinguished in it. 4th. Its fungous appearance, though white and soft, and the ease with which it is torn, are evident attributes of the mucous membranes. Every thing proves that the membrane of the tympanum, that of the meatus, &c. belong to the system of which we are treating. Thus in catarrhs of the pituitary membrane, and of that of the fauces, we most often find that the ear is affected; thus the ear is, like the mucous surfaces, the seat of hemorrhage, thus polypi arise in it, as in the nose and on the surface of the womb. We consider as a sign of deposition of pus in the ear, every purulent discharge coming from that cavity. But how can we conceive of a purulent collection in a part in which there is hardly any cellular texture, in a part wholly osseous? Besides the fibrous system, to which the periosteum of the tympanum belongs, hardly ever suppurates, as we know. Every thing then induces us to believe that these discharges are only the effect of a catarrh of the ear, a catarrh which is sometimes acute and sometimes chronic. I have moreover a recent and decisive fact upon this point; the body of a man subject to these discharges during life exhibited a remarkable thickness and redness of the membrane of the tympanum, but without the least trace of erosion. The ear suppurates like the urethra, the vagina, &c. it is not a new fluid which is formed by suppuration; it is that which naturally comes from the meatus which increases in quantity and comes through a preternatural opening of the membrane of the tympanum.

Diseases make the thickness of all the mucous surfaces vary remarkably. I have seen them many lines thick in the maxillary sinus, and nearly half an inch in the bladder. In great extensions of the mucous sacs, this thickness diminishes very much; it increases in their contractions. The stomach especially exhibits this phenomenon in these two opposite states.

The softness of the mucous corion is also very variable; in the nasal fossæ, in the stomach and the intestines, it is really a kind of organized velvet. The name of villous membrane is perfectly suited to it. On the contrary, at the origins of the mucous system, as in the mouth, upon the glans penis, at the entrance of the nose, it is a more dense and compact texture, approximating nearer in its nature to the cutaneous corion. I am persuaded that like this it might be tanned and be useful in the arts if it were in larger pieces, whilst I doubt if the action of tanning could produce an analogous phenomenon upon the mucous texture of the deep-seated organs. The softness of this would render it incapable of serving for external integuments. The least cause would be in fact sufficient to break and tear it. Its structure being different from that of the cutaneous corion is the reason that the variolus pustules never appear on it, whilst we often see them on the mucous surfaces near the openings of the skin, especially upon the tongue, the palate and the internal surface of the cheeks.

Exposed to the action of dry air, so that it may come everywhere in contact with it, it becomes dry and very thin, but preserves some resistance. In bladders inflated and dried, in the stomach, the intestines, &c. thus prepared, it is this texture which supports these organs, and which prevents them from becoming flat, though we permit the air to escape; it offers even a resistance, from which arises a kind of crepitation when we wish to bend them in various directions. To be convinced of this, it is only necessary to dry the mucous surface separate from the serous and muscular that correspond with it; these when dried remain pliable like the cellular texture, whilst the first has a kind of rigidity.

In the organs in which the redness of the mucous texture is slight, as in the bladder, the rectum, &c. it becomes transparent by drying. Where it is very red as in the stomach, it takes a deep tinge, which becomes even almost black if there had been an antecedent inflammation in it by which much blood had been accumulated; hence it appears that this fluid is the cause of the colour.

Thus dried the mucous surfaces are smooth; they lose their viscidity at least in appearance; their folds are effaced by adhering to the surface from which they arise; thus the valvulæ conniventes are marked in a dried intestine, only by a red line, without any apparent prominence. But if we macerate the intestines in this state, the folds form again and become visible.

Exposed to a moist air, or left with other flesh that will not allow it to become dry, the mucous corion putrefies with great ease; the odour that it then sends out is very fetid. I think the reason why the abdomen of dead bodies becomes putrid so soon is in part because it contains substances already in putrefaction, and also because the surfaces, in contact with these substances, and which by their vitality resisted before their action, then readily yield to them. If these substances were contiguous to aponeuroses, putrefaction would be much less rapid. The mucous system when putrid takes a greyish colour; and as the dense, subjacent cellular texture putrefies much less easily, we can then remove from it by the least pressure, the mucous corion, reduced to a putrid pulp, in which every trace of organization has disappeared, and which forms a real pap.

During life, gangrene of the mucous texture takes place in general less frequently than that of the cutaneous. The consequences of catarrh, compared with those of erysipelas may convince us of this; there are however cases in which death appears in this texture, whilst the surrounding ones continue to live, as in gangrenous angina.

Exposed to maceration, the mucous texture yields to it promptly. I think that next to the brain it is altered quickest by the action of water. It is then reduced to a reddish pulp very different from that from putrefaction in the open air. When we put the whole stomach to macerate, this pulp is detached, when the sub-mucous texture and the serous membrane have as yet undergone but little alteration.

Ebullition at first extracts from the mucous texture a greenish scum, very different from that which the muscular and cellular textures give when boiled. This scum which mixed with the whole fluid in the beginning of the boiling, disturbs it and renders it green at first, afterwards rises upon the surface where it has small bubbles of air mixed with its substance; it often even falls to the bottom of the vessel by its weight. Sulphuric acid changes the colour of it to a dull brown.

A short time before the water begins to boil, the mucous texture crisps and acquires the horny hardness like the others, but in a less degree however; hence why it is then wrinkled almost always in different directions. In fact, the sub-mucous texture upon which it is applied, contracting at that time much more than it, it must fold on account of its length; thus during life, when the fleshy coat of the stomach contracts, its mucous surface not contracting in proportion, produces the numerous folds of which we have spoken. The action of a concentrated acid crisping the sub-mucous texture more than the mucous itself, produces an analogous phenomenon. After having been a long time dried, the mucous texture, like however almost all those of the animal economy, does not lose the faculty of acquiring the horny hardness when it is plunged into boiling water; it exhibits this phenomenon, whether we expose it to it dry, or whether we do it after having first softened it in cold water. It is a means by which all the valvulæ conniventes may be made suddenly to reappear, which had disappeared by drying, and which form again the instant the intestine contracts. This experiment is very curious to witness.

When the ebullition has been a long time continued, the mucous texture turns gradually to a very deep grey, from the white which it had first become. It is not softer than in the natural state, but it breaks much quicker; the following experiment is a proof of it. If we draw the mucous corion, boiled for some time with the subjacent cellular texture, this last resists the most; so that it remains entire, whilst the mucous corion is broken in many places. This never assumes the gelatinous appearance of the cutaneous corion or the fibrous and cartilaginous organs when boiled and of the others which yield much gelatine. However by mixing a solution of tannin with the water in which this system taken from an adult has been boiled, I have seen an evident precipitate.

The action of the acids reduces to a pulp the mucous texture much sooner than most of the others. During life, all the caustics act much more rapidly upon it than upon the cutaneous, of which the thick epidermis is an intermediate organ which checks their tendency of combining with its corion. Thus the instant the nitric acid, a substance which common people almost always choose for their poison, as the practice at the Hôtel Dieu proves, thus the instant I say, that the nitric acid is in contact with the alimentary canal, it disorganizes it, it forms there a whitish eschar, which, when death does not take place immediately, as most often happens, is slowly removed and detached in the form of a membrane. We know that the lips gently rubbed with weakened nitric acid, become the seat of a troublesome itching, whilst that oftentimes though this acid may have acted upon the skin sufficiently to make it yellow, it does not suffer from it.

The softness of the mucous corion makes me presume that it is easily altered by the digestive juices, not that I confide in the experiments of Hunter, who pretended that these juices could act upon the coat that secretes them, but because in general I have observed that the textures like it yield very easily to the action of water in maceration and are also very easily digested. I have not however any experiment upon the subject, and we know that in the animal economy analogy is not always a faithful guide.

All the mucous surfaces, but especially that of the stomach and intestines, have the property of curdling milk, as have many other substances, especially the acids. Is it to this property that must be attributed a phenomenon which is constant during life, viz. the coagulation of milk that enters the stomach for digestion? or is this phenomenon owing to the mixture of this fluid with those which are secreted by the surface of this organ? I think that both these causes contribute to it at the same time; both separate produce in fact this phenomenon. Spallanzani has proved it as it respects the gastric juices. Every body knows that the mucous membrane dried, and consequently deprived of these juices, preserves the property of coagulating milk. Spallanzani has convinced himself that the serous and organic muscular systems of the stomach are destitute of it.

Are aphthæ an affection of the mucous corion? do they belong to the papillæ? are they seated in the glands? are they a separate inflammation of these glands, whilst catarrhs are characterized by a general inflammation of a considerable extent of the mucous system? All these questions deserve to be examined. Pinel has perceived the void there is in morbid anatomy upon this point.

_Mucous Papillæ._

The peculiar kind of sensibility which the skin enjoys is attributed principally, as we know, to what is called the papillary body, which commonly is not easy to be demonstrated. The sensibility of the mucous membranes, somewhat analogous to that of the skin, appears to me to have the same kind of organization, which is perceived with infinitely less ease. The papillæ of this system cannot be called in question at its origin, where it dips into the cavities, in the commencement even of these cavities, as upon the tongue, the palate, the internal part of the alæ of the nose, upon the glans penis, in the fossa navicularis, within the lips, &c. Inspection is sufficient to demonstrate them there. But it is asked if the papillæ exist also in the deep-seated parts of this system. Analogy indicates it, since the sensibility is as great there as at their origin, though with varieties that we shall point out; but inspection proves it in a manner not less certain. I think that the villi with which we everywhere see them covered are nothing but these papillæ.

Very different ideas have been entertained of the nature of these villi; they have been considered in the stomach and the œsophagus as destined to the exhalation of the gastric juice, in the intestines as serving for the absorption of chyle, &c. But, 1st, it is difficult to conceive how an organ everywhere nearly similar, can perform in different parts functions so different; I say nearly similar, for we shall see that these papillæ exhibit differences of length, size, &c. without having any of texture or structure. 2d. What can be the functions of the villi of the pituitary membrane, of the internal coat of the urethra, the bladder, &c. if they have not relation to the sensibility of these membranes? 3d. The microscopical experiments of Leiberkuhn upon the vesicle of the intestinal villi have been contradicted by those of Hunter, of Cruikshank and especially of Hewson. I am certain that I have never seen any thing similar on the surface of the small intestines, at the time of chylous absorption; and yet it would appear that a thing of inspection could not vary. 4th. It is true that these intestinal villi are everywhere accompanied by a vascular net-work, which gives them a red colour very different from the colour of the cutaneous papillæ; but the non-appearance of the cutaneous net-work is owing to the pressure of the atmospheric air, and especially to the contraction which it occasions in the small vessels. Observe in fact the fœtus as it comes from the womb of its mother; its skin is as red as the mucous membranes, and if its papillæ were a little longer, it would resemble almost exactly the internal surface of the intestines. Who does not know moreover, that the vascular net-work surrounding the cutaneous papillæ, is rendered evident by fine injections, so as to change their colour entirely?

That in the stomach this vascular net-work continuous with the exhalants furnishes the gastric juice, and that in the intestines it intermixes with the origin of the absorbents, so that these embrace the villi, we cannot doubt after the experiments and observations of anatomists who have recently engaged themselves in investigating the lymphatic system. But this does not prevent the base of these villi from being nervous, and them from performing upon the mucous membranes the same functions that the papillæ do upon the cutaneous organ. This manner of regarding them by explaining their existence generally observed upon all the mucous surfaces, appears to me to be much more conformable to the plan of nature, than to suppose them in each place with different and often opposite functions.

Besides it is difficult to decide the question by ocular observation. The delicacy of these elongations conceals their structure, even from our microscopical instruments, agents from which anatomy and physiology do not appear to me to have derived much assistance, because when we see obscurely, each sees in his own way and according to his own wishes. It is then the observation of vital properties that should especially guide us; now, it is evident to judge by them, that the villi have the nature I have attributed to them. The following experiment served to demonstrate to me the influence of the papillary body upon the cutaneous sensibility; it succeeds also upon the mucous membranes. Remove the epidermis in any part and irritate the papillary body with a sharp stilet; the animal is agitated, cries out and gives marks of acute pain. Slide afterwards, through a small opening made in the skin, a pointed stilet into the sub-cutaneous cellular texture, and irritate the internal surface of the corion; the animal remains quiet and makes no noise, unless some nervous filaments accidentally struck make him suffer. Hence it follows very evidently, that it is upon the external surface of the skin that its sensibility resides, that the nerves pass through the corion without contributing to its texture, and that their expansion takes place on the papillary body. It is precisely so with the mucous surfaces. Observe that this circumstance coincides very well with the functions of the two surfaces, which receive by their free portion the action of external bodies, to which they are foreign by their adhering portion.

The papillæ exhibit very great varieties. On the tongue, in the small intestines, in the stomach and in the gall-bladder, they are remarkable for their length. The œsophagus, the large intestines, the bladder, all the excretory ducts have those that are less evident; these last especially and the urethra in particular, are almost smooth in their whole mucous surface. We can scarcely distinguish the papillæ in the frontal, sphenoidal, maxillary sinuses, &c.

These small nervous eminences are sufficiently distinct and separate upon the tongue. In the nasal fossæ, the stomach and the intestines, they are so near together and at the same time so delicate, that the membrane has at first view an uniform and smooth appearance, though it is covered with these elongations. Each papilla is simple; no bifurcation is ever observed at its extremity. All appear to have a pyramidal form, if we can judge at least by those which are the most evident.

Are they susceptible of a species of erection? It has been believed with regard to those of the tongue, which become erect, it is said, to perceive tastes, and with regard to those of the nose, which receive odours more efficaciously in this state of erection, which is in the sensitive phenomena on a small scale, what the erection of the corpora cavernosa is on a large one. I do not believe that any exact experiment can prove this fact. Moreover, it would be necessary then that the intestinal, vesical papillæ, &c. should be in permanent erection, since they are almost always in contact with foreign substances.

II. _Parts common to the Organization of the Mucous System._

Besides the blood vessels, the exhalants and the absorbents which contribute to the structure of this system as to that of all the others, it exhibits also a common organ, which is found almost always separate elsewhere, but which is here especially designed for it. This common organ is of a glandular nature; we shall now examine it.

_Of the Mucous Glands and of the Fluids which they secrete._

The mucous glands exist in all the system of this name. Situated beneath the corion or even in its thickness, they pour out incessantly through imperceptible openings a mucilaginous fluid which lubricates its free surface, and which defends it from the impression of the bodies with which it is in contact, and at the same time favours the course of these bodies.