A mixture of equal parts gave the strychnine reaction very clearly, but the atropine reaction not at all; 1 strychnine with 3 of atropine gave strychnine reaction, but not that of atropine; 1 strychnine with 4 atropine gave indistinct reaction for both alkaloids; 1 of strychnine with 5 of atropine gave a momentary atropine reaction, the violet was, however, almost immediately replaced by a red colour. Vitali’s reaction was not clearly shown until the mixture was in the proportion of 9 of atropine to 1 of strychnine, but mixtures in the proportion of 3 strychnine and 1 atropine will give distinct mydriasis.
In such a case, of course, the strychnine should be separated from the atropine; this can be effected by precipitating the strychnine as chromate, filtering and recovering from the filter the atropine by alkalising and shaking it out with ether.
The atropine may be farther purified by converting it into oxalate, dissolving the oxalate in as small a quantity of alcohol as possible, and precipitating the oxalate out with ether; the precipitate is collected, dissolved in as small a quantity of water as possible, the water made alkaline, and the base shaken out with ether.
The most reliable test for atropine, or one of the mydriatic alkaloids, is its action on the iris; a solution of atropine, even so weak as 1 : 130,000, causing dilatation.[489] This action on the iris has been studied by Ruyter,[490] Donders, and von Graefe.
[489] De Actione Atropæ Belladonnæ in Iridem, Traj. ad Rhen., 1852.
[490] Arch. Ophthal., ix. 262, 1864.
The action is local, taking effect when in dilute solution only on the eye to which it has been applied; and it has been produced on the eyes of frogs, not only in the living subject, but after the head has been severed from the body and deprived of brain. The thinner the cornea, the quicker the dilatation; therefore, the younger the person or animal, the more suitable for experiment. In frogs, with a solution of 1 : 250, dilatation commences in about five minutes; in pigeons, seven minutes; and in rabbits, ten minutes. In man, a solution of 1 : 120 commences to act in about six to seven minutes, reaches its highest point in from ten to fifteen minutes, and persists more or less for six to eight days. A solution of 1 : 480 acts first in fifteen to twenty minutes, and reaches its greatest point in twenty minutes; a solution of 1 : 48,000 requires from three-quarters of an hour to an hour to show its effect. Dogs and cats are far more sensible to its influence than man, and therefore more suitable for experiment. If the expert chooses, he may essay the proof upon himself, controlling the dilatation by Calabar bean; but it is seldom necessary or advisable to make personal trials of this nature.[491]