GLUCOSIDES, gloo'ko-sidz, a class of complex vegetable substances which under the influences of heat, enzymes or chemical action produce a glucose. Most of the known gluco sides are derived from dextro-glucose, others from rhamnose or galactose. When the sugar is rhamnose they ate known as rhamnosides; if arabinose, they are known as arabinosides, etc. Glucosides containing rhamnose require a spe cific enzyme to effect their hydrolysis. There are a great many glucosides in nature, and within recent years a large number have been made artificially. The chemical composition of the artificial glucosides is well understood, since they are the result of synthesis, but the make up of the natural glucosides is not clear. From comparison with the synthetic glucosides, how ever, it has been generally accepted that natural glucosides are formed by the elimination of water between a hydroxyl group of the sugar and one from the other compound. Although present in plants in very small quantities, glu cosides play a very interesting role in nature. By reason of their bitterness and 9f often being poisonous, they preserve seeds from de struction by animals, man included, until they shall have ripened, and then on germination plant enzymes or ferments acting on the gluco sides set free a certain amount of sugar, which is of much service to the young developing plant. An excellent illustration of theirpro tective qualities is seen in persimmons, which, when green, are so puckery by reason of the glucoside tannic acid that they are left severely alone. When ripe, however, the tannic acid is converted largely into sugar, and the fruit, then eaten and carried about by animals, can dis tribute its seed.
Glucosides are obtained by extracting the plant substance with water or alcohol. It is necessary, in most cases, to destroy the accom panying enzyme when water is used as a sol vent, otherwise the glucoside is destroyed dur ing the process. The glucosides generally are colorless, crystalline substances having a bitter taste. A typical example is amygdahn, of the bitter almond, and the kernels of peach stones. The larger part of the glucosides belong to the class known as asapoiuns" from their resem blance to the specific glucoside obtained from the root of the Saponaria rubs°. The sapo nins are nearly all colloidal substances dissolv ing freely in water, and yielding a froth when the solution is shaken, and produce soapy emul sions with fats and oils. They are insoluble in alcohol, ether and benzol. From their aqueous solutions the saponins are precipitated by add ing ammonia sulphate. Although one or two of the saponins are useful in the arts (as in bottled soda water and ginger beer, to hold the froth) they are practically all of a poisonous nature. A curious use is made of some of them in the East, where they are strewn upon the surface of shallow waters, with the effect of killing the fish therein: the very small por tion of poison taken in by the fish does not make it unfit for human food. Another im
portant class of the glucosides, though much fewer in numbers than the saponins, are the cyanogenetic glucosides, thus named because they yield hydrocyanic acid as one of the products of hydrolysis. They are found in flax and sorghum, and in some of the laurels, magnolias and roses, as well as in other repre sentatives of some of the higher orders of plants. The significance of the glucosides in the plant economy is not known, and eminent authorities differ in their opinions upon this question. In most, perhaps in all, cases the glucoside is accompanied in the plant by its appropriate enzyme, which is able to hydro lyse it. They do not exist in the same cell, but are brought together by the breaking down of the cellular structure. Observation has shown that salicin is formed in the willow during daylight, but after the light has gone the salicin is split into sugar and the alcohol saligenin, by the activity of salicase.
The more important glucosides are antyg dalin — of bitter almonds; prunasin — of wild cherry; stonbunigrin— of the common elder; arbutin — of the barberry; phloridzin — of the bark of apple and pear trees; salicin —of willow bark; populin —of the poplar; coniferin —of fir trees; sittigrin —of black mustard; and indican — of the indigo plant. It is interesting to note in passing that in several instances cultivation of wild plants has had the effect of reducing the contained glucoside to an almost unrecognizable quantity. Many ghi cosides are affected by heat. Some are split by cooking in water, but a boiling temperature is apt to destroy the action in many. Thus it is necessary to use cold water if one desires to obtain the volatile oil of mustard in making a mustard plaster. Many fungi are capable of breaking down glucosides, which fact is of a great deal of practical importance in medicine, for some active remedies which contain gluco sides, if kept too long on the druggist's shelf, develop molds within them. These destroy the active principle of the drug and thus render it useless. In medicine the most important glu coside containing drugs belongs to what is known as the °digitalis group."' Thus digitalis contains four or five, strophanthus two, apocy num two, and squills the same number. These bodies are all heart tonics in small doses and heart poisons in larger amounts. Consult Arm strong, E. F.,