This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Sialagogues are medicines which increase the secretion of saliva, and of the mucus of the mouth and fauces. There are two divisions of them; one operating through the system, the other by direct contact with the buccal mucous membrane.
1. There are many substances which more or less increase the secretion of saliva, when taken internally, but very few which do so regularly, or to an amount which would render their employment for this effect desirable. The only medicines which could be relied upon as sialagogues, internally administered, are the preparations of mercury, which appear to exercise a peculiar influence over these glands, though much of their effect must be ascribed to the stomatitis produced by them; inflammation of the mouth operating as a powerful stimulus to the salivary secretion. it is, however, quite unnecessary to pursue our inquiries, in this place, into the sialagogue operation of internal medicines, as none of them are prescribed for their effects in this way, not even the mercurials; and, in relation to the several individual substances having more or less of the property, their possession of it has been alluded to when they have been elsewhere treated of.
It is a fact, however, of some interest, that the sensation of nausea is usually attended with a copious secretion of saliva, and that emetic substances are, consequently, in general, very efficient sialagogues. Mental influence, also, has often great effect in stimulating this function. Every one is familiar with the effect of the mere idea of food, especially when the appetite is somewhat keen, in promoting the flow of saliva. The mouth of the hungry man "waters" at the sight or thought of an approaching meal. it is not impossible that such influences may sometimes be brought to bear advantageously upon the function, as a therapeutic measure. Thus, in cases of the monomania-cal, who purpose to starve themselves to death, a plate of food set before them, and allowed to remain, sometimes overcomes an obstinacy which refuses to yield to solicitation or menaces. in examining the tongue as an index of the state of the system, if we find the mouth dry, we can often succeed, by causing the patient to close his mouth, and move the tongue about, in inducing sufficient secretion to render the parts moist. in such a case, we may infer that the dryness was owing to some comparatively trivial cause; as, in the healthful state, the very thought and effort on the part of the patient provoke the action of the glands; whereas, if the function had been suppressed by some general morbid influence, it would scarcely return upon such gentle solicitation. I have often been enabled to deduce somewhat important practical inferences, as to the state of the system, from this simple experiment.
2. It is only the local sialagogues that are practically employed, and that we are now to consider. These act by an irritant impression on the membrane, which calls the mucous follicles directly into increased action, and the salivary glands indirectly through the sympathy which connects them with the mouth. Any irritant may thus prove siala-gogue; and even the act of mastication, though exercised upon a perfectly bland and tasteless object, will have more or less of the effect. As substances used in this way are generally chewed, they are called not unfrequently masticalories. Those actually employed remedially are always more or less irritant, and some of them very powerfully so.
They operate therapeutically in three ways; first, as direct stimulants to the parts with which they come into contact; secondly, by depletion from the secreting vessels; and thirdly, by revulsion from neighbouring parts.
1. In reference to the first method of action, they may be used advantageously in debilitated or paralytic states of the tongue, fauces, or mouth generally. Loss of taste or of motor power in the tongue, relaxation of the uvula from weakness, and difficulty of deglutition from palsy of the fauces, may sometimes be relieved in this way, provided the affection has become quite local, or is not associated with acute disorder of the nervous centres.
2. Through their depletory influence they may relieve inflammatory conditions of the neighbouring parts, especially painful rheumatic inflammation of the jaws and face, and inflammations not rheumatic of the sockets of the teeth, and of the antra, especially somewhat chronic in their character. Masticatories often prove of considerable service in inflammatory toothache.
3. By revulsion they act beneficially in the same affections, as also in neuralgic conditions of the face, and inflammation of parts somewhat more distant, as in chronic tumefactions of the salivary glands themselves, and similar affections of the Eustachian tube, the larynx, the eyes, ears, and nostrils. in chronic hoarseness from inflammation of the larynx, and deafness from closure of the Eustachian tube, considerable advantage may sometimes be derived from irritant impressions made on the fauces by these medicines. As the saliva, impregnated with the soluble principles of the masticatory, is swallowed, it has some effect on the stomach also; and this must always be taken into consideration in recommending these medicines.
The substances most frequently used as local sialagogues, are tobacco, Ginger Root, Horse-Radish, Mezereon, and Pellitory. These have already been considered, with the exception of the last, which requires a brief notice.