The physiological test consists in administering the substance to some small animal (preferably to a frog), and inducing the ordinary tetanic symptoms. It may be at once observed that if definite chemical evidence of strychnine has been obtained, the physiological test is quite unnecessary; and, on the other hand, should the application of a liquid or substance to a frog induce tetanus, while chemical evidence of the presence of strychnine was wanting, it would be hazardous to assert that strychnine was present, seeing that caffeine, carbolic acid, picrotoxin, certain of the opium alkaloids, hypaphorine, some of the ptomaines, and many other substances induce similar symptoms. The best method (if the test is used at all) is to take two frogs,[449] and insert under the skin of the one the needle of a subcutaneous syringe, previously charged with a solution of the substance, injecting a moderate quantity. The other frog is treated similarly with a very dilute solution of strychnine, and the two are then placed under small glass shades, and the symptoms observed and compared. It is not absolutely necessary to inject the solution under the skin, for if applied to the surface the same effects are produced; but, if accustomed to manipulation, the operator will find the subcutaneous application more certain, especially in dealing with minute quantities of the alkaloid.[450]
[449] A very practical disadvantage of the physiological test is the great difficulty of obtaining frogs exactly when wanted.
[450] Methyl strychnine, as well as methyl brucine, has been shown by Brown and Fraser to have an effect exactly the opposite to that of strychnine, paralysing the muscles like curare. In the case, therefore, of the methyl compounds, a physiological test would be very valuable, since these compounds do not respond to the ordinary tests.
§ 399. Hypaphorine.—One substance is known which neither physiological test nor the colour reactions suffice to distinguish from strychnine, viz., hypaphorine,[451] the active matter of a papilionaceous tree growing in Java—the Hypaphorus subumbrans; a small quantity of the alkaloid is in the bark, a larger quantity is in the seed.
[451] Dr. C. Plugge, Arch. f. exp. Path. u. Ph., Bd. xxxii. 313.
Hypaphorine forms colourless crystals which brown, without melting, above 220°, and exhale a vapour smelling like napththylamine. The free alkaloid is soluble in water, but has no action on litmus. The salts are less soluble than the free alkaloid, so that acids, such as nitric or hydrochloric, produce in a short time precipitates on standing. Solutions of the salts are not precipitated by alkalies; chloroform, ether, benzene, all fail to extract it from either alkaline or acid solutions. It gives no precipitate with potassic chromate, but most general alkaloidal reagents precipitate.