In general, I think that there are but few systems which deserve, more than this of which we are treating, to fix the attention of physicians, on account of the innumerable alterations of which it is susceptible, alterations which almost always suppose those of the predominant vital properties of this system, as the alterations of the muscular, nervous systems, &c. most often put in action the properties which more particularly belong to them, viz. animal contractility for one, and the sensibility of the same species for the other. The sensible organic contractility does not appear to be the attribute of the mucous system; yet there is often in it something more than the insensible oscillations which compose the other organic contractility. For example, in the emission of semen, in which there is no agent of impulse at the extremity of the urethra, as in the evacuation of urine, it is very probable that this is spasmodically contracted to produce the jet, oftentimes very strong, which then takes place. The following phenomenon which I have observed in myself appears to belong to the same cause. In gaping, there sometimes escapes from the mouth then wide open, a small jet of fluid, which coming from the lateral parts of this cavity that it passes over, is thrown at some distance; if a surface is then before the mouth, as when we read a book, this fluid is spread in small drops upon this surface; it is the saliva which the excretory duct of Steno throws out with force. Now on the one hand this duct is almost wholly mucous, and on the other it has not at its posterior part a muscular agent of impulse. Perhaps the excretories which pour out their fluids in the deep parts of the organs, exhibit the same phenomenon. We know that the milk is also sometimes subject to a kind of ejection, when it is very abundant, an ejection which supposes a powerful contraction of the lactiferous ducts. In general, these different motions analogous to that of the dartos, of the cellular texture, &c. appear to hold a middle place between those of tone and those of irritability. _Sympathies._ There are few systems that sympathize more frequently with the others than this. Now in its sympathies, it sometimes influences and sometimes is influenced. The first Tissot calls the active mode of sympathy, the second the passive. Let us make use of this classification. _Active Sympathies._ One point of the mucous system being inflamed, irritated or stimulated in any way, all the vital forces can enter separately into action in the other systems.