Читать книгу Treatise on the Anatomy and Physiology of the Mucous Membranes - Bichat Xavier - Страница 3

8. Every mucous membrane presents two surfaces; the one adhering to the adjacent organs; the other free, beset with villosities, and always moist with a mucous fluid: each of them deserves a particular attention.

9. The adherent surface is attached to muscles almost throughout its extent. The mouth, the pharynx, the whole of the alimentary canal, the bladder, the vagina, the uterus, and part of the urethra, &c. present a muscular bed, embracing the exterior of their mucous coat. In animals that have the panniculus carnosus, this disposition perfectly coincides with that of the skin, which, as we shall see, is in other respects analogous in structure to mucous membranes. In man the cutaneous organ presents here and there traces of this exterior muscle, as we observe in the platysma myoides, the palmaris brevis, the occipito frontalis, in most of the muscles of the face, &c. This disposition of mucous membranes places them under the influence of those habitual changes of contraction and dilatation, which are favourable to their secretion, and various other functions.

10. This muscular bed is not immediately inserted into the exterior surface of the mucous membranes, but rather, according to Albinus, into a dense layer of cellular tissue, which all the ancient authors have denominated, in the stomach, intestines, and bladder, the nervous coat; but when well examined it presents no character analogous to that which the name indicates. The experiment of inflation, by which it is brought into its primitive state, is not so easy as Albinus and others have pretended; which led me to think that its nature might not be cellular, but that it was probably of a fibrous texture, formed by a web of extremely delicate and scarcely visible tendons, offering points of origin and insertion to all the fleshy fibres of the muscular bed, which, as we know, never describe entire circles, but rather different segments of that curve. I confess that this conjecture, though very likely, is not founded upon any decisive and rigorous experiment.

11. Whatever may be the nature of this intermediate membrane to the mucous and muscular coats, it evidently has a dense, close texture, which gives it a resistance very analogous to one of the fibrous membranes. It is from this that the organ receives its form; it is this which maintains and controls its shape, as may be proved by the following experiment. Take a portion of intestine: remove in any part of the bowel a part of this membrane, with the serous and muscular membranes: having applied a ligature to the inferior end, inflate it, the air will produce in the denuded part an hernia of the mucous coat. Take another portion of intestine, turn it, dissect off a small part of the mucous membrane and of this coat: inflation will produce upon the serous and muscular coats the same phenomenon as in the preceding case it did in the mucous membrane. It is therefore to this intermediate tunic that the mucous membrane owes its power of resistance to substances which distend it. This applies equally to the stomach, bladder, œsophagus, &c.

12. The free surface of mucous membranes, or that which is continually moistened by the fluid from which they borrow their name, presents two kinds of wrinkles or folds, the one inherent in their structure and which is constantly present, whatever may be their state of contraction or dilatation, such as the pylorus, the valvula conniventes, the valve of the colon, &c. These folds are formed, not merely by the mucous membranes, but also by the intermediate membrane mentioned above, and which in these parts takes a remarkable density and thickness.

13. The other folds may be called accidental, and are only observed during the contraction of the organ; such are those of the inner surface of the stomach, and of the large intestines, &c. In most of the human subjects brought to our amphitheatres, these folds in the stomach, of which so much has been said, are not perceptible, because generally the subject has died of a disease which has impaired the vital powers, without preventing all the action of this viscus; so that, although it is frequently found empty, its fibres are not in the least contracted.

14. In experiments on living animals, on the contrary, these folds are very apparent; and observe how they may be demonstrated. Let a dog eat or drink copiously; open it immediately, and make an incision into the stomach the whole length of its greater curvature, no fold will then appear, but it soon contracts, its edges are drawn in, and the whole of the mucous surface is covered with numerous prominent plicæ in the form of circumvolutions. The same result may be observed in the stomach of a recently killed animal by distending it with air, and then opening it; or, what is still better, by laying it open whilst empty, and stretching it, the folds will disappear, and when we cease to make the extension they immediately form again and are very apparent.

15. I would observe on the subject of inflating the stomach, that by distending it with oxygen gas the application of this fluid does not produce more prominent folds, and therefore no stronger contraction, than when carbonic acid gas is used for the same purpose. This experiment presents a result very similar to what I have observed when I have rendered animals emphysematous by different æriform fluids. Frogs and Guinea pigs (these are the two kinds I have chosen, the one being an animal of red and cold, and the other of red and warm blood) presented very little difference in their irritability, or their Galvanic susceptibility, whether inflated with oxygen gas or with carbonic acid gas. They live very well with this artificial emphysema, which gradually disappears. Inflation with nitrous gas is always mortal, and its contact appears to strike the muscles with atony. The stomach distended with it very soon loses its power of contracting, and its folds disappear. Here, as in all the experiments which have the vital powers for their object, we frequently obtain very variable results.

16. It follows, from what we have said respecting the folds of mucous membranes, that in the contraction of the hollow organs, which are lined by them, they suffer but a very trifling diminution of surface, they scarcely contract at all, but fold themselves within; so that in dissecting them upon their contracted organ, we have an extent of surface nearly equal to that which they present during its dilatation. This assertion, which is true concerning the stomach, the œsophagus, and the intestines, is, perhaps, not quite so as respects the bladder, whose contraction does not show within such prominent folds, but they are sufficiently marked to bring the mucous membrane of this organ under the general law. It is, also, nearly the same with the gall bladder; yet we find here another cause; observed alternately, in a state of hunger and during digestion, it will be found to contain double the quantity of bile in the former case that it does in the latter, as I have had the opportunity of seeing in numerous instances, in experiments made with this object in view, or with other intentions. Now, when it has evacuated part of its contents it does not contract upon the remainder of the bile, with the energy of the stomach when it contains but little food, nor with the power of the bladder when it contains but a small quantity of urine, but is then flaccid, so that its distention or nondistention has but very trifling influence upon the folds of its mucous membranes.

17. Moreover, in saying that the mucous membranes present with trifling variation the same extent of surface in the dilatations as during the contraction of their respective organs, I intend to speak of the ordinary state of the functions only, and not of those enormous dilatations which are frequently seen in the stomach and bladder, more rarely in the intestines. In such cases there is doubtless a real extension, which in the membrane coincides with that of the organ.

18. One remarkable observation that the free surface of mucous membranes affords us, and which I have already pointed out, is, that this face is everywhere in contact with bodies of a different nature to that of the animal: these bodies are either introduced from without for its nourishment, and are not yet assimilated to its substance, as we see in the alimentary canal and in the trachea, or they are produced within, as we observe in the excretory ducts of the glands, which all open into cavities lined by mucous membranes, and discharge those particles, which, after having for some time formed a part of the composition of the solids, become heterogeneous to them, and are thrown off by that habitual action of decomposition, which takes place in living bodies. According to this observation we must consider the mucous membranes as defensive coats, placed between our organs and foreign bodies, and that they consequently serve the same purpose internally which the skin does externally, as respects bodies that are in contact with it.