The mucous membranes by the continual secretion of which they are the seat, enjoy a principal part in the animal economy. We ought to consider them as one of the great emunctories by which the residue of nutrition constantly escapes, and consequently as one of the principal agents of the habitual decomposition which removes from living bodies the particles that, having for some time contributed to the composition of the solids, are afterwards to become heterogeneous to them. Observe in fact that the mucous fluids do not enter the circulation, but go out of the body; that of the bladder, the ureters and the urethra, with the urine; that of the vesiculæ seminales and the different ducts with the semen; that of the nostrils by the act of blowing the nose; that of the mouth, in part by evaporation and in part by the anus with the excrements; that of the bronchia, by pulmonary exhalation, which arises principally, as I shall say, from the solution of this mucous fluid in the inspired air; those of the œsophagus, the stomach, the intestines, the gall-bladder, &c. with the excrements, of which they often form in the ordinary state a part almost as considerable as the residue of the aliments, and which they even compose almost entirely in some cases of dysentery and fever, in which the quantity of matter voided is evidently disproportioned to that taken in, &c. Let us observe upon this subject that there are always some errors in the analyses of the fluids in contact with the membranes of which we are speaking, as in that of the urine, the bile, the gastric juices, &c. because it is very difficult and even impossible to separate the mucous fluids from them. If we recollect what has been previously said upon the extent of the two general mucous surfaces, which is equal and even superior to the extent of the cutaneous organ, and if we afterwards consider that these two great surfaces are constantly throwing out mucous fluids, we shall perceive how important this evacuation must be in the economy, and of what mischief its derangement must become the source. It is undoubtedly to this law of nature which wishes to have every mucous fluid thrown out, that must be attributed, in part in the fœtus, the presence of the unctuous fluid of which the gall-bladder is full, the meconium which loads the intestines, &c. fluids which appear to be but a mass of mucous juices, which being unable to pass off, remain until birth, without being absorbed, upon the respective organs on which they have been secreted.