/\ customary to indicate this formula by a plane hexagon, thus | |. \/ It is understood, in all such cases, that the figure represents six carbon atoms arranged in a closed ring, with alternate double and single bonds, and with a hydrogen atom attached to each carbon. The printing of some other group as OH, CH_{3}, adjacent to an angle of the hexagon means that this group replaces the H atom in the compound which is being illustrated. HYDROLYSIS OF THE NATURAL GLUCOSIDES All natural glucosides are hydrolyzed into a sugar and another organic residue by boiling with mineral acids; although they vary widely in the ease with which this hydrolysis is brought about. In most cases, the glucoside is easily hydrolyzed by an enzyme which occurs in the same plant tissue, but in different cells than those which contain the glucoside. Injury to the tissues, germination processes, and perhaps other physiological activities of the cells, result in bringing the enzyme in contact with the glucoside and the hydrolysis of the latter takes place. A large number of such enzymes have been found in plants, many of which hydrolyze only a single glucoside. However, two enzymes, namely, the emulsin of almond kernels, and _myrosin_ of black mustard seeds, each hydrolyze a considerable number of glucosides. In general, _emulsin_ will aid in the hydrolysis of any glucoside which is a derivative of [beta]-glucose, and myrosin will help to split up any sulfur-containing glucoside. Glucosides which are derivatives of rhamnose require a special enzyme, known as _rhamnase_, for their hydrolysis. The following reactions for the hydrolysis of arbutin and of amygdalin are typical of this action, and will serve to illustrate the general structure of these compounds: ------O------- | | CH_{2}OH·CHOH·CH·CHOH·CHOH·CH·O·C_{6}H_{4}OH + H_{2}O Arbutin = C_{6}H_{12}O_{6} + HOC_{6}H_{4}OH Glucose Hydroquinone C_{6}H_{5} | (_a_) C_{6}H_{11}O_{5}·O·C_{6}H_{10}O_{4}·O·CH + H_{2}O Amygdalin | CN C_{6}H_{5} | = C_{6}H_{11}O_{5}·O·CH + C_{6}H_{12}O_{6} Mandelo-nitrile | Glucose glucoside CN