MUCUS (from p,qa, the secretion of the Schneiderian membrane). This word has been used in so very indefinite a sense by the members of the medical profession, that animal chemists have had great difficulty in fixing on any distinctive characters by which the sub stance might be identified. The great source of confusion appears to have been that phy siologists and the profession generally have applied the adjective mucous or mucoid to certain forms of secreted matter; from which circumstance the term mucus has gradually advanced into substantive use as a medicb-chemical word, embracing in its mean ing the secretions from the mouth, nose, in testines, Ste. as though these were identical in their chemical characters. We shall pre sently show, however, that such is not the case.
In the Philosophical Transactions for 1800 Mr. Hatchett published a paper, in which he endeavoured to show that such a principle as mucus really existed, characterised by pecu liar properties ; but considered it a modified form of gelatin. Dr. Bostock subsequently published a paper in Nicholson's Journal, in which he showed that mucus differed from 1 gelatin; this he proved by demonstrating that tanning did not precipitate mucus, though gelatin was immediately thrown down by it, whereas diacetate of lead precipitated mucus copiously, without affecting gelatin: bichloride of mercury and ferrocyanuret of potassa did not precipitate either mucus or gelatin. I shall show hereafter that these last-mentioned re actions do not apply to every form of mucus : the ingenious experiments of Dr. Bostock can indeed no longer be considered pertinent, in asmuch as the researches of modern chemists have gone far to prove that gelatin is rather a product than an educt of animal analysis. The experiments of Dr. Bostock were made on the saliva of the mouth, and some sub sequent observations by Mr. Brande made on the same secretion showed that the precipitates obtained by the diacetate of lead and nitrate of silver consisted of the chlorides and phos phates of those metals; a fact which inclined Mr. Brande to consider mucus as a compound substance rather than a proximate element, and induced him to apply electricity as a means of decomposition. From the results obtained
in this inquiry, Mr. Brande was inclined to consider mucus as a compound of albumen either with pure soda or chloride of sodium.
Dr. Marcet made some experiments on mucus which induced him to believe that several morbid secretions contained it as a constituent; he considered it to be present in dropsical effusions. Berzelius, though he allows the secretions of the mucous membranes to differ in chemical character, and to possess distinct properties according to the especial office they have to fulfil in lubricating par ticular parts, still believes that such a proximate element as mucus really exists as one of the constituents of such secretions, and notices it in his analysis of mucus of the nose. In considering this subject it is, therefore, neces sary to premise that the general term, as used by the medical profession, has no relation whatever to the chemistry of the question, the secretions of the different mucous mem branes varying greatly in chemical composition, but, notwithstanding, presenting a physical character in common, in relation to which the term mucous has been applied to them. The inquiry of greatest interest consists in determining whether there exists a peculiar proximate element in virtue of which the mucous character is developed, or whether, on the other hand, the peculiar physical character can be traced to the presence of some combi nation of albumen which is common to all mucous secretions, notwithstanding that they may differ greatly in other respects. We have already seen that the latter opinion is supported by Mr.Brande's experiments, while Berzelius, on the contrary, seems to favour the former view of the case. Before entering upon this question I shall describe the chemical characters of several secretions from mucous surfaces, as the reader will then be better prepared for the inquiry. I shall commence with the secretion from the nose, since this may be regarded as the type of those viscous products to which the general name of mucus has been applied.