The mandelo nitrile glucoside contains an asymmetric carbon atom which is wholly outside its glucose group, thus C_{6}H_{10}O_{5}-O-C_{6}H_{5}·CH·CN. Hence, it may exist in dextro, levo, and racemic forms. In the amygdalin molecule, it exists in the dextro form, which has been named "prunasin." The levo form, known as "sambunigrin," has been obtained by hydrolysis of a compound isomeric with amygdalin, whose composition has not been definitely worked out; while the racemic form, known as "prulaurasin," has been prepared from isoamygdalin, by the action of alkalies. Hence, all the possible compounds indicated by the presence of the asymmetric carbon have been found and identified. The crude enzyme preparation which is obtained from almond seeds, known as "emulsin," contains two enzymes, _amygdalase_, which breaks the amygdalin molecule at linkage (1), and _prunase_, which breaks it at (2). The action of amygdalase must always precede that of prunase. In other words, it is never possible to break off a disaccharide sugar from the molecule, either by the action of prunase alone, or by means of any other hydrolytic agent. =Dhurrin=, C_{14}H_{17}O_{7}N, is another glucoside of fairly general occurrence in plants, which yields HCN as one of the products of its hydrolysis. It is found in the leaves and stems of several species of millets and sorghums. Frequent cases of poisoning of cattle from eating of these plants as forage have been reported. On hydrolysis, dhurrin first yields glucose and paraoxy-mandelo nitrile; the latter then breaks down into paraoxy-benzaldehyde and HCN. =Vicianin=, C_{19}H_{25}O_{10}N, is a cyanophoric glucoside, found in the seeds of wild vetch, etc. On hydrolysis, it yields glucose, arabinose, and _d_-mandelo nitrile. It is, therefore, similar to amygdalin, except that one glucose molecule is replaced by arabinose. THE MUSTARD OIL GLUCOSIDES The seeds of several species of plants of the Cruciferæ or mustard family contain glucosides in which the other characteristic group is a sulfur-containing compound. These glucosides yield "mustard oils" when they are hydrolyzed by the enzyme _myrosin_, which accompanies them in the plant. The following glucosides, found in the seeds of white and black mustard, are the best-known representatives of this class. =Sinigrin=, C_{10}H_{16}O_{9}NS_{2}K, found in black mustard seeds, when hydrolyzed yields glucose, acid potassium sulfate, and allyl isosulfocyanide (mustard oil), as indicated by the equation. C_{10}H_{16}O_{9}NS_{2}K+H_{2}O = C_{6}H_{12}O_{6} + C_{3}H_{5}N[trb]C=S+KHSO_{4}. The acid potassium sulfate group separates first and most readily, leaving a compound known as _merosinigrin_, for which the following formula has been suggested: