§ 431. Effects of Aconitine on Animal Life.—There are few substances which have been experimented upon in such a variety of ways and upon so many classes of animals as aconitine in different forms; but there does not seem to be any essential difference in the symptoms produced in different animals save that which is explained by the organisation of the life-form under experiment.
Insects.—The author has made experiments with the active principles of aconite upon blow-flies. An extract was made by allowing the ordinary tincture to evaporate spontaneously at the temperature of the atmosphere. If a minute dot of this is placed upon the head of a blow-fly, absorption of the active principle takes place in from fifteen to thirty minutes, and marked symptoms result. The symptoms consist essentially of muscular weakness, inability to fly, and to walk up perpendicular surfaces; there is also, in all cases, a curious entanglement of the legs, and very often extrusion of the proboscis; trembling of the legs and muscular twitchings are frequent. A progressive paralysis terminates in from four to five hours in death; the death is generally so gradual that it is difficult to know when the event occurs, but in one case there were violent movements of the body, and sudden death.[476]
[476] It may be well to quote in full a typical experiment. Six P.M., a little extract smeared on the head of a blow-fly. Forty-five minutes after—makes no attempt to fly, great muscular weakness, no trembling or convulsive movements. Fifty minutes after—partial paralysis of right half of body, so that the fly, on moving, goes in a circular direction, the second pair of legs are curiously bent forward and useless; the wings seem fairly strong. Seventy-five minutes—fly very dull, always in one spot, without movement; when placed on a horizontal glass surface, and the glass then very slowly inclined, until it is at last quite perpendicular, the fly falls. There is now a strange entanglement of the legs. 125 minutes—perfectly paralysed; 145 minutes—dead.
Fish.—The action on fish has been studied by Schulz and Praag. There is rapid loss of power and diminished breathing; the respiration seems difficult, and the fish rapidly die.
Reptiles—Frogs.—The most recent experiments on frogs are those of Plugge, and although his interpretation of the phenomena in some points is different from that of previous observers, the symptoms themselves are, as might have been expected, not different from those described by Achscharumow, L. v. Praag, and others. Plugge found no qualitative difference in the action of any of the commercial samples of aconitine. This fact gives the necessary value to all the old experiments, for we now know that, although they were performed with impure or weak preparations, yet there is no reason to believe that the symptoms described were due to any other but the alkaloid aconitine in varying degrees of purity or dilution. Frogs show very quickly signs of weakness in the muscular power; the respiration invariably becomes laboured, and ceases after a few minutes; the heart’s action becomes slowed, irregular, and then stops in diastole. The poisoned heart, while still pulsating, cannot be arrested either by electrical stimulation of the vagus or by irritation of the sinus, nor when once arrested can any further contraction be excited in it. Opening of the mouth and apparent efforts to vomit, Plugge observed both with Rana esculenta and Rana temporaria. He considers them almost invariable signs of aconitine poisoning. A separation of mucus from the surface of the body of the frog is also very constantly observed. Dilatation of the pupils is frequent, but not constant; there may be convulsions, both of a clonic and tonic character, before death, but fibrillar twitchings are seldom. (With regard to the dose required to affect frogs, see ante, [pp. 355] and [356].)
Birds.—There is a discrepancy in the descriptions of the action of aconitine on birds. L. v. Praag thought the respiration and circulation but little affected at first; while Achscharumow witnessed in pigeons dyspnœa, dilatation of the pupils, vomiting, shivering, and paresis. It may be taken that the usual symptoms observed are some difficulty in breathing, a diminution of temperature, a loss of muscular power generally (but not constantly), dilatation of the pupils, and convulsions before death.
Mammals.—The effects vary somewhat, according to the dose. Very large doses kill rabbits rapidly. They fall on their sides, are violently convulsed, and die in an asphyxiated condition; but with smaller doses the phenomena first observed are generally to be referred to the respiration. Thus, in an experiment on the horse, Dr. Harley found that the subcutaneous administration of ·6 mgrm. (·01 grain) caused in a weakly colt some acceleration of the pulse and a partial paralysis of the dilator narium. Double the quantity given to the same animal some time after, caused, in six hours and a half, some muscular weakness, and an evident respiratory trouble. The horse recovered in eighteen hours. 2·7 mgrms. (1⁄24 grain) given in the same way, after a long interval of time, caused, at the end of an hour, more pronounced symptoms; the pulse, at the commencement 50, rose in an hour and a half to 68, then the respiration became audible and difficult. In an hour and three-quarters there were great restlessness and diminution of muscular power. Two hours after the injection the muscular weakness increased so much that the horse fell down; he was also convulsed. After eight hours he began to improve. In another experiment, 32·4 mgrms. (1⁄2 grain) killed a sturdy entire horse in two hours and twenty minutes, the symptoms commencing within the hour, and consisting of difficulty of breathing, irregularity of the heart’s action, and convulsions.