From these varieties in the vital forces of each division of the mucous system, it is not astonishing that the diseases of this system should also be very variable. Each has a general character, but this is modified in each mucous surface. There is an order of symptoms common to all catarrhs; but each has its peculiar signs, each has its different products. The fluid from a pulmonary catarrh does not resemble that from a nasal one; that coming from a urethral, vesical catarrh, &c. is wholly different from that from an intestinal one. These fluids exhibit in their morbid changes the same differences that we have pointed out in their natural composition, differences which are derived like them, from the different vitality of each portion of the mucous system.
It is to these varieties of life and the vital forces that must be referred also those of the sympathies. Each portion of this system has a peculiar sympathetic action upon the other organs. The pituitary alone being irritated produces sneezing. You would excite in vain the extremity of the glans penis, the rectum, &c. you would never produce vomiting as you do by stimulating the uvula.
An important remark should here be made in regard to the stomach. We know that there is no organ which performs a more important part in the sympathies than this. The least affection of this important viscus, the least gastric derangement, spread over the whole animal economy a painful influence; all the other parts feel it. I do not believe even that there is any uneasiness more fatiguing and general than that which we then experience in certain cases. The general weakness which takes place in hunger almost instantaneously, is sympathetic; the alteration of nutrition has not had time to produce it. The same is true with regard to the sudden increase of the forces which results from the contact of the aliments upon the mucous surface of this viscus, an increase which cannot be attributed to the passage of the chyle into the blood, which has not yet had time to take place.
I think the stomach owes this important part in the sympathies principally to its mucous surface. In fact, 1st, its serous surface has no connexion with it, since it is there of the same nature as in all the rest of the peritoneum, besides in what is called inflammation of the abdomen, and in which this serous surface is especially affected, we do not observe such numerous sympathetic relations. 2d. The fleshy coat appears to be the same as that of the whole intestinal canal; why then should it have different influences? 3d. As it respects blood-vessels and nerves of the ganglions, the stomach is nearly organized like the rest of the alimentary tube. 4th. It has besides the par vagum; but is this nerve alone capable of producing such numerous phenomena? It can contribute to them; but certainly the peculiar modifications which it experiences in the mucous surface, the peculiar nature of this membrane contribute also much to it. No membrane is organized like that of the stomach. Though we do not see perfectly at first view its organic differences, reflection is sufficient to convince us of them; thus on the one hand no one separates so great a quantity of fluid, and on the other none furnishes one of a nature analogous to that of the gastric juice.
ARTICLE FOURTH.
DEVELOPMENT OF THE MUCOUS SYSTEM.
I. State of the Mucous System in the First Age.
The development of the mucous system follows in general the laws of that of the organs to which it belongs. Early in the gastric apparatus, later in the pulmonary and that of generation, it seems in its growth rather to obey the impulse it receives, than to give one to what surrounds it, an arrangement common to almost all the systems which contribute to form the different apparatus. Observe in fact that there is always in the growth certain parts to which all the others refer; thus in the cerebral apparatus, the early size of the brain produces that of the bones of the cranium, of the dura-mater, the pia-mater, the arachnoides and the vessels; thus it is on account of the spinal marrow, that the vertebral canal is so evident in the fœtus; thus all the serous surfaces have a growth in proportion to that of their respective organs, &c. &c. I would remark however that the early growth of the systems which are only to follow that of the parts to which they are destined, is only in the dimensions of length, breadth, &c. The thickness most commonly does not correspond with these dimensions. Thus the bones of the cranium though broader in proportion than those of the pelvis in the fœtus, are not thicker. The extent of the dura-mater is in proportion greater than that of the albuginea which belongs to the same system; but the organization is no further advanced.
In the fœtus, the delicacy of the mucous texture is extreme, the papillæ are hardly perceptible. But by carrying the hand over a mucous surface, we feel there an extremely delicate velvet and such as is not equalled by the finest velvet. The redness of this system is not then as evident, because no doubt less blood penetrates it, as the various functions which are afterwards to take place upon these surfaces, as digestion, the excretions, respiration, &c. are but feeble or entirely wanting. At this age, the quantity of blood seems to be in an inverse ratio in the skin and in these surfaces. The mucous red is then like the muscular, of a very deep tinge, often even livid, on account of the nature of the blood circulating in the arteries. Then the adhesions of the mucous texture to the subjacent cellular are less; those especially of this last with the surrounding parts are very slight; thus it is very easy to draw out whole the internal portion of the intestines of the fœtus, from the external covering that contains it, so as to see two cylindrical canals, one of which is muscular and serous, the other cellular and mucous. The stretching destroys in this experiment all the valvulæ conniventes, and the small intestines are as smooth on the interior as the large, in the canal artificially extracted. If we subject this canal to ebullition, much more scum arises from it than in the adult; this scum is white and never green. The crisping that takes place a little before the first boiling, diminishes more in proportion the length of the canal, and consequently appears to be stronger.
At birth, when respiration and digestion suddenly commence, the secretions increase, the mucous system acquires a remarkable degree of activity. It is instantly excited powerfully by the many new substances with which it is in contact. It is by it and by the cutaneous system that bodies foreign to ours then immediately stimulate it, and so much the more efficaciously, as the double surface which receives the excitement is not accustomed to it. Then the red blood which penetrates the mucous system, gives it an increase of energy and sensibility, which renders it still more proper to receive impressions. Thus the mucous juices which till then stagnated upon their respective surfaces, without fatiguing and irritating them, are suddenly for them, on account of their increase of sensibility, stimulants which excite them, and force the subjacent muscles to contract. Then the urine becomes for the bladder a cause that promotes the contraction of it. A few instants after birth, all the openings in which the mucous membranes begin, open and permit to escape the meconium, the urine and all the mucous juices. This internal and general shock that empties all the mucous cavities, renders them fit to become the seat of the great functions which are soon to take place in them.