General Anatomy, Applied to Physiology and Medicine, Vol. 3 (of 3)

by Xavier Bichat

Constantly in relation, like the integuments, with external bodies, the mucous surfaces have occasion for a sensibility which would enable the mind to perceive these relations, especially at the origin of these surfaces. Thus the animal sensibility is very much developed there. It is even superior in it in many places to that of the cutaneous organ, in which no sensation is as acute as those which take place on the pituitary membrane from odours, upon the palatine from tastes, upon the surface of the vagina, the urethra, the glans penis during coition. But without speaking of these exaggerations of sensibility, if I may so express myself, all the natural phenomena of the mucous surfaces prove this property in an evident manner; it is unnecessary however to pause for these phenomena.

I would only observe that this sensibility, like that of the cutaneous organ, is essentially subjected to the powerful influence of habit, which tending constantly to blunt the acuteness of the sensation of which they are the seat, brings equally to indifference the pain and the pleasure they make us experience, and of which it is the medium, as we know. 1st. I say that habit brings to indifference the painful sensations arising upon the mucous membranes. The presence of a sound in the urethra for the first time, is distressing the first day, painful the second, inconvenient the third, and insensible the fourth. Pessaries introduced into the vagina, bougies into the rectum, tents fixed in the nasal fossæ, and a canula kept for a length of time in the nasal canal, exhibit in different degrees the same phenomena. It is upon this remark that is founded the possibility of the introduction of sounds into the wind-pipe to aid respiration, and into the œsophagus to produce an artificial deglutition. This law of habit can even transform into a pleasure an impression at first painful; the use of snuff for the pituitary membrane and different aliments for the palatine, furnish well known examples of this. 2d. I say that habit brings to indifference agreeable sensations arising on the mucous surfaces; the perfumer, placed in an odoriferous atmosphere, the cook, whose palate is constantly affected by delicious tastes, do not find in their professions the acute enjoyments they give to others. From habit can even arise the succession from pleasure to painful sensations, as in the preceding case it converts pain to pleasure.

I would however observe that this remarkable influence of habit is only exerted upon sensations produced by simple contact, and not upon those produced by real injuries, as the tearing, the forced stretching, the cutting or pinching of the mucous system; thus it does not mitigate the pains caused in the bladder by pressure and by the tearing a stone occasions, or on the surface of the womb, of the nasal fossæ, &c. by a polypus, on that of the œsophagus or the wind-pipe by a sharp and uneven body accidentally lodged there, &c. &c.

It is to this power of habit over the sensibility of the mucous system, that must be in part referred the gradual diminution of its functions, which accompanies age. Every thing is stimulant in infancy, every thing is blunted in old age. In one, the very active sensibility of the alimentary, biliary, urinary, salivary surfaces, &c. contributes principally to produce that rapidity with which the digestive and secretory phenomena succeed each other; in the other, this sensibility blunted by habitual contact, connects but slowly the same phenomena.

Is it not from the same cause that arises this remarkable modification of the sensibility of this system, viz. that at its origins, as upon the pituitary, the palatine membranes, the œsophagus, the glans penis, the opening of the rectum, &c. it gives us the sensation of the bodies with which it is in contact, and that it does not give this sensation in the very deep organs which it lines, as in the intestines, the excretories, the gall-bladder, &c.? In the interior of the organs, this contact is always uniform; the bladder only knows the contact of the urine, the gall-bladder that of the bile, the stomach that of the aliments masticated and reduced, whatever may be their diversity, to an uniform, pulpy mass. This uniformity of sensation produces no perception, because in order to perceive, it is necessary to compare, and here the two terms of comparison are wanting. Thus the fœtus has no sensation of the waters of the amnios; thus, the air, very irritating to a new born infant, becomes insensible to it. On the contrary, at the beginning of the mucous membranes, the stimulants vary every instant; the mind can then perceive the presence of them, because it can establish approximations between their different modes of action. What I say is so true, that if in the interior of the organs, the mucous membranes are in contact with a foreign body, different from that which they are accustomed to, they transmit the sensation of it to the mind. A catheter in the bladder, sounds introduced into the stomach, &c. are examples of this. Fresh air, in great heat of the atmosphere, suddenly introduced into the trachea, carries an agreeable sensation over the whole surface of the bronchia; but habit soon renders us insensible to it and we cease to have the perception of it. Yet it is to be observed that when the intestines come out in preternatural inversions of the anus, their sensibility never becomes so acute as that of the palatine, pituitary surfaces, &c. &c. The absence of cerebral nerves no doubt has an influence upon this phenomenon.

The sensibility of the mucous system is much raised in inflammations; acute catarrhs are, as we know, very painful. The contact of bodies is then not only felt, but is very disagreeable. I would observe however that the sensibility never rises so high as it does in the inflamed cellular, serous, fibrous systems, &c. A phlegmon, a pleurisy, &c. compared with a catarrh, are sufficient to convince us of this. We may say that the organs least accustomed to feel in the natural state, experience in diseases the most acute sensations.

There is no animal contractility in the mucous system.

Properties of Organic Life.

Organic sensibility and insensible contractility are very evident in the mucous system. They are constantly put in action in it by four different causes; 1st, by the nutrition of this system; 2d, by the absorption that takes place in it, either naturally or accidentally; 3d, by its exhalation; 4th, by the constant secretion of its glands. These two properties are the original causes of all these functions, the increase and diminution of which are truly the indices of the state of these glands. As a thousand causes continually act upon the mucous surfaces, as a thousand different stimuli continually excite them, especially at their origin, this state is incessantly varying like the functions that result from it.

The mucous system differs then from most of the others; 1st, in this, that the organic sensibility and the insensible contractility are habitually more exalted in it, on account of the more numerous functions over which they preside; 2d, in this, that they incessantly vary, on account of the variety of the stimuli. Observe in fact that, in the osseous, fibrous, cartilaginous, muscular, nervous systems, &c. on the one hand, these properties are put in action only by nutrition; and on the other, no stimulant being in contact with these systems, they always remain at the same degree.