The characters and physiological action of commercial aconitia vary greatly, as might be expected from the ununiformity of its composition.
SEPARATION AND TESTS.
For the extraction and separation of aconitia from anima matters, the modification of Stas’s general method, described on page 5 (Chap. I.), may be employed. The alkaloids of aconite being, as has been already shown, very liable to decomposition, great care must be taken, during the extraction with alcohol and subsequent evaporation of the extracts, that the temperature does not rise above 50° C.: the use of mineral acids should also be avoided.
Tests.—1. The residue of aconitia or pseudaconitia, obtained on spontaneous evaporation of the anhydrous chloroform solution, will generally be found to be more or less crystalline, when examined under the microscope.
2. The Taste Test.—A minute portion of the residue, either alone or dissolved in a small quantity of water acidulated with acetic acid, should be rubbed with the finger on the lips and gums, or cautiously applied to the tip of the tongue. If aconitia or pseudaconitia be present, a peculiar tingling and numbness will be quickly experienced in and around the parts to which the alkaloidal extract has been applied: salivation, with a desire to expectorate, and a sense of swelling at the back of the throat, are also frequently noticed. The effects, or some of them, usually last from three to six hours, or even longer. This action is peculiar to aconite; the test, therefore, is of the utmost value, and one which must never be omitted.
3. The Physiological Test.—Inject a small quantity of the alkaloidal extract, dissolved in a little water acidulated with acetic acid, into the back of a mouse or other small animal. In the event of aconitia being present, characteristic symptoms of aconite poisoning are manifested in a few minutes, and the death of the animal rapidly ensues. Among the chief symptoms observed by Dr. Fleming, in some experiments upon animals, made in 1844, were “weakness of the limbs, staggering, a gradually increasing paralysis of the voluntary muscles, loss or diminution of sight, slowness of pulse, difficulty of breathing, occasional convulsive movements, in two cases opisthotonos, contracted pupils, but often dilating two or three minutes before death, and death by asphyxia.” (Woodman and Tidy’s For. Med., p. 394). This test is also a very important one.
4. Chemical Tests.—Solutions of salts of aconitia and pseudaconitia are precipitated by most of the general reagents for alkaloids, such as Mayer’s reagent, tannic acid, potassium tri-iodide, phosphomolybdic acid, &c. Platinic chloride, picric or carbazotic acid, and auric chloride, however, do not give precipitates, except in concentrated solutions. Among the special tests for aconitia and pseudaconitia which have been described, the following may be mentioned. (A) With sulphuric acid, no change takes place in the cold, but on warming, a pale yellow, deepening into brown, and finally changing into violet-red, is observed. This reaction varies very greatly with different samples of aconitia, and little or no reliance can be placed upon it as a toxicological test. (B) With sulphuric acid and a drop of saturated solution of sugar, a fine rose-red colour, passing into dingy brown, has been obtained. Experience, however, has not shown this test to be of any especial value. (C) If cautiously heated for ten or fifteen minutes on the water-bath with a few drops of syrupy phosphoric acid, aconitia is said to yield a violet or blue colour. This reaction is uncertain and therefore useless: it may be obtained with impure samples, while pure aconitia and pseudaconitia fail to give it. Mr. T. B. Groves (Year-Book of Pharmacy, 1873) says:—“The colour reactions of these alkaloids may be dismissed in a word. There are ‘none.’ As for the phosphoric acid reaction producing a blue colour, I have never succeeded in obtaining it. It is probably due to some accidental impurity, and I believe Dr. Flückiger has arrived at the same conclusion.”
Hence, as there are no reliable, characteristic, and distinctive chemical tests for aconitia, its presence or absence must be judged chiefly from the results of the tests of taste and physiological action on small animals. A substance, previously proved to be an alkaloid by its yielding precipitates with most of the general reagents for alkaloids, and which, when applied to the tongue and injected under the skin of a small animal, produces the effects already described, is absolutely certain to be aconitia.
HISTORY, PREPARATIONS, AND DOSES.