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

by Xavier Bichat

It should be observed in regard to the pulmonary perspiration, that the solution of the mucous fluid which lubricates the bronchia, in the air constantly inspired and expired, furnishes a considerable portion of this vapour which, insensible in summer, is very evident in winter, on account of the condensation of the air. The mucous juices are dissolved like every other fluid; for wherever there is atmospheric air, heat and moisture, there is evaporation. Here this evaporation is even a means which nature employs to rid herself, as I have said, of the mucous juices. If they are too abundant, as in a cold, then the quantity of air which serves as a vehicle to them, not increasing in proportion, it is necessary that there should be another mode of evacuation; this is expectoration which compensates for what the air cannot remove by solution.

The intestinal juice which Haller has especially considered, but which appears to be in much less quantity than he thought it, the œsophagean and gastric juices, particularly this last which has been supposed to be distinct from the mucous juices, are probably deposited by exhalation upon their respective mucous surfaces. But in general it is very difficult to distinguish with precision what belongs in these organs to the exhalant system, from that which is furnished by the system of mucous glands, which, as we have said, are everywhere subjacent to them. Thus we constantly see the mucous fluids of the œsophagus, the stomach and the intestines, mixing with the œsophagean, gastric and intestinal fluids.

As on the one hand the blood vessels ramify almost naked on the mucous surfaces, and as on the other these vessels are always the origin of the exhalants, it is evident, that these have but a short course to run to arrive at their surfaces; they are rather pores than distinct vessels. Hence why no doubt the blood has so great a tendency to escape by the exhalants; why consequently hemorrhages without rupture are so frequent in the mucous system; why this affection can be classed in the diseases of this system, &c. &c. No other, by the arrangement of the arteries, offers to the exhalants so short a course between their origin and termination. Often even, as I have said, we make the blood of these vessels ooze in the dead body through their exhalants.

Absorbents.

The absorption of the mucous membranes is evidently proved, 1st, by those of chyle and of drinks on the intestinal surfaces, of the venereal virus upon the glans penis and the canal of the urethra, of the variolous when the gums are rubbed with it, of the serous portion of the bile, the urine and the semen, when they remain in their respective reservoirs. 2d. When, in the paralysis of the fleshy fibres that terminate the rectum, substances are accumulated at the extremity of this intestine, these substances often become hard, an effect probably of an absorption of the soft parts. 3d. There have been various cases in which the urine has been almost wholly absorbed by the mucous surface of the bladder, where there have been insurmountable obstacles in the urethra. 4th. If we respire, by means of a tube, the air of a large vessel filled with the exhalations of turpentine, so that these vapours can only act upon the mucous surface of the bronchia, the urine has the peculiar odour that always arises from the use of this substance, the exhalations from which have been introduced into the blood by the means of absorption, &c.

Whatever may be the mode of this absorption, it appears that it does not take place in a constant and uninterrupted manner, like those of the serous membranes, in which the exhalant and absorbent systems are in a regular and continual alternation of action. There is scarcely any but the chylous absorption, that of drinks, and that of the aqueous portion of the secreted fluids remaining in a reservoir as they come from their glands, that constantly take place. Nothing is more variable than the other absorptions. Under the same influence, the glans takes up or leaves the venereal virus; the internal surface of the bronchia sometimes admits and sometimes refuses admittance to contagious miasmata. There are more cases of retention in which the urine is not absorbed entirely, than there are where this absorption takes place, &c. &c. The innumerable varieties of the vital forces of the mucous membranes, varieties produced by those of the stimuli with which they are in contact, explain these phenomena. If these forces are raised or diminished a little, the absorption is altered, even that which is natural, as that of the chyle. Take a purgative; it contracts, shuts even the mouth of the absorbents of the intestinal canal; as long as the irritation continues, all the drinks that are taken pass off by the anus; at the end of four or five hours, the absorbents gradually recover their natural tone and absorption recommences. In these cases, the first discharges are only the intestinal matters, the others are the copious drinks that have been taken. There are many diseases in which, the sensibility of the chylous absorbents being too much raised, they are no longer in relation with the aliments, they take up with difficulty the residue of them, &c. Deficiency of action produces the same phenomenon; in absorption in fact it is a middle degree of sensibility of the organ which produces it, a degree below or above which it cannot take place.

All the mucous absorbents appear to go to the thoracic duct.

Nerves.

I would remark that at all the origins of the mucous system, where the animal sensibility is very great and where it places us, like the skin, in relation with external bodies, cerebral nerves are distributed. The pituitary and palatine membranes, the conjunctiva, the mucous surface of the rectum, the glans penis, the prepuce, &c. exhibit this fact very evidently. There are hardly any nervous filaments coming from the ganglions in these different places.

On the contrary, this last species of nerves is the predominant one in the intestines, in all the excretories, in the reservoirs of the secreted fluids, &c. places where the organic sensibility is the most evident.