ON THE MYDRIATIC ALKALOIDS. By ALBERT LADENBURG. We translate the following important article, says the _Chemists' Journal_, from the _Moniteur Scientifique_ of last month. It may be explained for the sake of our student readers that the word _mydriatic_ is derived from the Greek _mudriasis_, which means paralysis of the pupil. The synthetical researches which I have undertaken with a view to explain the constitution of atropine have shown me the necessity of studying the connection of atropine with the other alkaloids, which have an analogous physiological action. According to the early researches we could not discover any of these relationships which only become evident when we come to study the new discoveries which have been made in connection with the tropines, to which class belong both duboisine and hyoscyamine, which, although differing from atropine, are equally mydriatic in their action. I.--ATROPINE. Discovered by Mein in 1831 in the roots of belladonna. More thoroughly studied some time after by Geiger and Hesse, who confirmed Mein's results. Liebig next published an analysis of the alkaloid, which was afterward shown to be incorrect. He consequently modified his formula, and gave the following as the composition of atropine; C_{17}H_{23}NO_{3}. Liebig's amended analysis was afterward confirmed by Planta, who further showed that the alkaloid itself melted at 194° F., and its double gold salt at 275° F. It is worthy of remark that the first figure was considered correct until my researches proved the contrary. The physiological action of atropine, especially in relation to the eye, has been most carefully studied by several celebrated ophthalmologists, such as Graef, Donders, Bezold, and Bloebaum. Its chemical properties have also been the object of very extensive researches by Pfeiffer, Kraut, and Lassen. Pfeiffer first discovered that benzoic acid was one of the products of decomposition of atropine, and Kraut split atropine by means of baryta water into atropic acid, C_{9}H_{6}O_{2}, and tropine, C_{8}O_{15}NO. Lassen, who used hydrochloric acid, discovered the true products of the splitting up of atropine, viz., tropic acid, C_{9}H_{8}O_{3}, and tropine, C_{8}H_{15}N, and proved at the same time that atropic acid is easily formed by the action of boiling baryta water on tropic acid, while hydrochloric acid at all temperatures forms isatropic acid, an isomer of atropic acid. Kraut confirmed these results, and showed that atropic acid as well as cinnamic acid gives benzoic acid by oxidation, and hydratropic acid (the isomer of phenylpropionic acid) by reduction with sodium amalgam. These results are sufficient to show that tropic acid may have one of the following two formulae. I II CH_{2}OH CH_{3} / / C_{4}H_{5}CH or C_{8}H_{5}--C--OH \ \ OOHO COOH