IN a former paper' it was shown that the two hyoseyamines differ to a marked extent in their pharmacological action, the laevorotary natural base possessing a very powerful action on the terminations of the nerves in the salivary glands, heart, and iris, while the dextrorotary artificial base is almost devoid of effect on these organs, but exercises a stronger stimulating action on the central nervous system of the frog. The action of atropine (racemic hyoscyatmiine) is the resultant of the action of its two components, lavo-and dextro-hyoseyamine, and it thus affects the nerve terminations about half as strongly as levo-hyoscyamine, while possessing a more distinct stimulant action on the central nervous system. The difference in the effect of-lhevo-hyoscyamine and the dextrorotary alkaloid was first inferred from a comparison of the actioif of atropine and hyoseyamine, and was then confirmed by the study of dextro-hyoscyamine.A review of the literature concerning the action of optical isomers on vertebrates was given in that paper but two further examples of differentiation between the isomers have since been added. Mayor2 states that levo-nicotine, the natural alkaloid, is twice as toxic to guineapigs as the artificial dextro-nicotine. The lavorotary base irnduces pain when injected hypodermically, while the dextrorotary has nio such effect, and there appears to be some difference in the nature of the convulsions, those following dextro-nicotine having a prevailing tremulous character, while those induced by levo-nicotine are more violent and set in more abruptly. Neuberg and Mayer3 found that d-mannose' undergoes more rapid oxidation in the tissues of the rabbit than 1-mannose, and that the injection of inactive mannose is followed by the appearance of 1-and inactive mannose in the urine. Glycogen is formled from inactive