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.