This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
Glycerin plays an inconspicuous role as a food. It is mainly useful for its sweetish taste as a substitute for sugar in the diet of diabetics, but to many persons the taste of glycerin itself is nauseous. It is now largely superseded by saccharin. It is highly hygroscopic, and if taken in the mouth undiluted makes the mucous membrane sticky and unpleasant, but it is used as a mouth wash in a diluted form in the proportion of a drachm to the ounce of water. The mouth may be rinsed or swabbed with it in cases of acute fever, such as typhoid, where the mucous surface has become dried or the tongue is glazed or fissured. It acts by protecting the mucous membrane from evaporation, making the mouth more comfortable. In such cases it sometimes diminishes thirst, although its effect in this respect is very uncertain. Glycerin is also laxative, and it may be given either per os or in the form of the well-known glycerin suppositories for the purpose of increasing peristaltic action and evacuating the bowels.
It is also used as an enema.