The chemical characters of the substance which Berzehus notices in this analysis as " mucus" are as follows. It is not soluble in water, but swells up and becomes transpa rent. When dried it is again capable of being swelled by water; but after this experiment has been repeated several times it becomes of a yellow colour, and assumes somewhat the appearance of pus. When boiled in water it neither hardens nor contracts ; but after this treatment it is found, to a certain extent, to have lost its property of swelling. When dry it is of a yellow colour and transparent. By distillation it yields carbonate of ammonia and empyreumatic animal oil. The ashes obtained from this substance yield phosphate and car bonate of lime, with traces of carbonate of soda. This mucus is soluble in weak sulphuric acid ; the strong acid darkens its colour and even tually destroys its texture. Weak nitric acid co agulates it superficially and renders it partially yellow : long digestion in this acid causes its solution. Acetic acid contracts it, but does not dissolve it even when assisted by heat. It dissolves from it, however, a portion of albumen, which renders the solution preci pitable by the ferrocyanuret of potassium. Caustic potash renders this mucus more tena cious, but by digestion it dissolves it. In fusion of galls coagulates it when dissolved in acids or when swelled by water. These characters described by Berzehits may be re cei% ed as the general properties of that substance to which mucous secretions owe their viscous character.
Urinary MUCVS.—This form of mucus is best obtained by allowing recently voided urine to remain at rest in a tall glass vessel, when the mucus will subside after some hours, and may be collected by pouring off the super natant fluid as nearly as possible without disturbing tire precipitate, and throwing the remaining part of the secretion on a filter ; the mucus will now be retained on the paper. Its properties are as follows :—when dried on paper it exhibits a bright surface ; on being moistened, however, it rapidly assumes its original appearance. It is insoluble in sul phuric acid, but the nitric and acetic acids dissolve it in large proportion, and the solution is precipitable by ferrocyanuret of potassa: caustic potassa in solution dissolves it entirely.
Salivary mucus.—The saliva, as it passes from the mouth, contains, in all probability, two kinds of mucus ; one derived from the mucous membrane lining the mouth, and the other from the internal membrane of the salivary ducts. %Then saliva is allowed to stand it very soon separates into two parts ; one a supernatant liquor of a slightly milky hue, and the other a deposit of a white colour, which in this state does not exhibit the ordinary physical characteristics of mucus. On pouring
off the liquor, however, and then agitating the deposit with water, it immediately assumes the glairy character; indeed, without the addi tion of water it will exhibit a mucoid tenacity if an attempt be made to raise it from the vessel in which it has collected. The liquor which has been poured off from this dense form of the principle still contains a portion of mucus in suspension, which may be ob tained by dilution with water, and may pro bably be a less coherent form of mucus secreted by the lining membrane of the salivary ducts. These two forms of mucus have much the same chemical characters, being insoluble in water and coagulable, and rendered firmer, by the acetic, hydrochloric, and sulphuric acids. The liquors obtained by digesting these acids on mucus are not precipitable by the addition of alkalies, which shows that this form of the secretion does not contain any free subphosphate of lime. It is dissolved by caustic alkalies and precipitable by the acids when thus dissolved : the solution in alkalies, however, is not complete, a residue being always obtained, which is soluble in acid, but which cannot be precipitated from the acid solution by means of caustic alkali, and, therefore, is not an earthy salt. Notwith stauding this, however, we can always obtain evidence of the existence of phosphate of lime in considerable proportion by incinerating mucus ; and Berzelius considers the tartar formed on the teeth to be derived from this source. This form of mucus is considered by Berzelius to approach very nearly to that obta.ned from the stomach and intestines: it differs greatly from nasal mucus, which is soluble in the sulphuric and nitric acids.
1 nle:4 inal mucus.—The mucus of the stomach and intestines can be best obtained by washing the mucous surfaces of those organs taken from an animal that has fasted some hours : it is occasionally observed adhering to ex crement. This mucus, when dried, is no longer capable of assuming the tenacious character on being moistened with water, but, according to an observation of Berzellus, re quires an alkaline solution for that purpose : it is coagulable by the acids. The acetic acid acts powerfully upon it, solidifying it com pletely. None of the acids dissolve it ; the acetic acid seems, however, to have a partial action, since tire liquor obtained by digesting it is precipitab'e by the addition of infusion of galls, but not always. by the feirocyanuret of potasia. The caustic alkalies dissolve this mucus, and the addition of acids precipitates it when thus brought into solution.
4ilueas uf the gall-bladder has been examined, and appears to resemble that last described ; it is insoluble in the acids and precipitable by them from solution in alkalies.