SECT. 7.
The Liquor that is separated from these Glands is a Mucilage, not unlike the White of an Egg, tho’ not always so clear and pellucid; when pure it is very like it. In some Animals it is of a Colour inclining to Yellow, and is composed of watry, saline and slimy Particles; it is supposed that the earthy Particles may be about a two and thirtieth Part. The Nature of this Mucilage seems nearly to approach to that of the Serum of the Blood, separated from the grumous Part upon being exposed to the Air, and exhibit much the same Appearances upon Trials by Mixture with other Bodies, only the Serum is not so mucilaginous. The Serum is coagulated upon being mixed with Spirit or Oyl of Vitriol, Spirit of Salt, Oyl of Sulphur, and other acid Spirits. The Serum, upon being held in a Spoon over the Fire, becomes a thick Jelly, and at length a sort of friable Glew; on the contrary, the Mucilage grows thinner, upon the same Application, throws up a slight thin Film at Top, and produces but a slight Coagulum. After the aqueous Parts are evaporated, there remains scarce a thirtieth Part of the whole Mass.
SECT. 8.
The principal Use of this Mucilage is to lubricate the Joints, and to render and preserve the Extremities of the Bones, at their Articulations, smooth and supple, for the easy Performance of animal Motion. Besides this mucilaginous Liquor from these Glands, there is an oily medullary kind of Substance transmitted through the very Bone into the Cavity of the Joints: These two Liquors are mixed by the Motion of the Joints, the Mucilage contributes to make the Oyl more slimy, and the Oyl preserves the Mucilage from stiffening into a Jelly. This Mucilage further serves to prevent the Extremities of the Joints from being burnt up in the Gout. In the same Manner the Muscles and Tendons are lubricated and kept in Vigour by the Liquor supplied from the same kind of Glands placed on their Membranes.
SECT. 9.
This Mucilage is formed from the purer Part of the Lymph and the serous Parts of the Blood, and separated in these Glands from the Mass of the Blood. In order to have a more distinct Notion of its constituent Parts, and to know how it comes to occasion the Gout, the following Experiments of Dr. Havers may be very properly repeated in this Place. He made most of the Trials both when it was hot and when it was cold. Vinegar dropt into it, when it was hot, made a considerable Coagulation with a Serum; it must be observed that those Mixtures that were made with it cold, did produce the same Effect when it was warmed, namely a Coagulation with Acids and Stypticks, only in an higher Degree: And whereas the Coagulations, which were made when it was in one State, did only change it into a thick Jelly without any Serum, after the Manner of a Cheese when it is newly set, as they term it, which over the Fire afterwards exhibited two distinct Parts, a Coagulum and a Whey; in the other, that is, when the Mucilage was hot, the Mixtures which coagulated it produced an harder Curd, and a Serum distinct from it. By dropping in some of the Decoction of Galls into it, the whole turned into a gelatinous Mass, and it was all a Sort of Coagulum like a Skin, of a whitish Colour, and so tough as to hang all together when it was taken up with a Needle. This Coagulum or Jelly being laid in the Sun, and dried, the Parts of it stuck all together in one Piece, but was very friable and easily rubbed to a Powder, which was very much like fine Flower. The same Effect had the strong Infusion of Balaustia, red Roses, Pomegranate Bark, and the Peruvian Bark, although there was some Difference in the Coagulation, according to the different Degrees of their Astringency. With a few Drops of Aqua Fortis distilled upon it, the Mucilage was immediately coagulated, though the Coagulum, which was white, was so tender, that it would by Agitation be dissolved in fair Water, and make it of the same Colour almost like Milk; Spirit of Nitre made exactly the same Alteration in it as Aqua Fortis did, a Coagulum which was of a white Colour. Vinegar, Spirit of Salt of Vitriol, Oyl of Vitriol, and of Sulphur in some Mucilage which I tried it with, did not make any considerable Alteration when it was cold, but in some other it did more; when Aqua Fortis and Spirit of Nitre did produce in all the same Effects in the same Degree. It was mighty observable, that so strong an Acid as Oyl of Vitriol should have no greater Effect upon it to alter it not, so considerable as that of Vinegar, which would incline one to think that it is not always the high Degree of Acidity that works this Change. But there seems to be something particular in Wines, which disposes them to coagulate this Liquor, when any of them are made Use of; and those Parts of them, which are apt to act thus upon it, are cast into those Interstices where they have the Mucilage singly to work upon. And therefore we find how readily any Wines do procure the Paroxysms of the Gout, where the Tone of the Glands is weakned, and the Patient hath a Disposition to this Distemper; which agrees with those Trials I have made with some of them: For Claret, white Wine, and even Sack, but the Claret especially, did make a Coagulum like a Jelly; and it was not strange that Claret, which hath both an Acid and a Stypticity in it, should produce the greatest Coagulation. A mercurial Water made of Sublimate and Aqua Calcis, made a very considerable whitish Coagulation, and rendred it all a thick Jelly, which being held over the Fire, turned to a Curd and a Serum. A Solution of Roman Vitriol produced a Coagulation likewise; so did Allum dissolved in Water, but it made a greater Alteration in some than it did in others, though the Mucilages were taken from subjects of the same Species. Saccharum Saturni did inspissate it, which appeared to be a true Coagulation, because with the Fire they would turn to a distinct Coagulum and Serum. Salt of Wormwood made no sensible Alteration, only it seemed a little thicker, to which I put some of the Decoction of Galls, which immediately produced a Coagulation. Upon dropping in some Spirit of Vitriol, to see what would be the Effect of the Colluctation of the Salt and Spirit, and I found, after it was over, that the Coagulum and the serous Part were distinguished, and the Serum limpid like Water. I took some of the Decoction of Galls, and added to it Spirit of Vitriol, intending to make a strong Acid austere, where I observed that these two by themselves produced a strong Coagulation; and stirring of them together, to see if the whole might not be brought to mix by that Means, I found the Coagulum turned into a viscous Body, and a perfect soft Gum. Then I took out the Gum, and poured some Mucilage to the residuous Liquor, by which it was changed so as to assume a whitish Colour, but was not considerably coagulated; which it was the less, because the austere Parts were most of them, with some of the Acid, precipitated into the Gum which had been separated from the serous Part. But if the Spirit of Vitriol and the Mucilage are first mixed, and the austere Liquor be afterwards added, they make a very considerable and plentiful Coagulum, which will only be broken into smaller Parts, and not be dissolved in Water. Aqua Fortis, and the Decoction of Galls being both dropt into some of the Mucilage, made a white Coagulum, which likewise was not dissolved in Water, altho’ with oleum Tartari per Deliquium, and so with Spirit of Sal Ammoniac dropt into it, I presently dissolved it. I found likewise, that the Coagulum made with the Infusion of Pomegranate Peel, red Roses and Balaustia, being mixed with some of the Mucilage, to which an Acid had been put, made the Coagulum more firm, so that it would not dissolve in fair Water; but yet the Oyl of Tartar by Deliquium, and the Spirit of Sal Ammoniac, did the Business in all of them. The Coagulum of the Mucilage made with an Acid, and the Infusion of the Peruvian Bark and several other Astringents, I kept and dried, which when they were first put to the Teeth, seemed a little gritty, though after they were moist they were of a softer Nature. All the Mixtures made of the Mucilage with an Acid and an Austere, produced not only a plentiful Coagulation of a white Colour, but such a one as was of a thicker Consistence, and not Soluble in fair Water, as that was which was made with an Acid only.
