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ELEMENTS OF MATERIA MEDICA.

Seeds lose the power of germination by immersion in this acid. In thoseparts of lactescent plants which are poisoned by it, the milky juice doesnot flow from the cells or vessels in which it is contained. By chemicalmeans it has been shewn that the acid becomes absorbed (Decandolle,Physiol. Veget. p. 1357). Ammonia has, in some cases, appeared tofavour the recovery of plants which had been exposed to the vapour ofthe acid (Macairc, op. cit.).

( b.) On animals generally. —Hydrocyanic acid is an energetic poisonto all classes of animals. Experiments have been made with it onthe following:— Mammalia, Aves, Reptilia, Amphibia, Pisces, Gaste-ropoda, Annelida, Crustacea, Insecta , and Infusoria (Conllon, quoted byWibmer, Wirkung d. Arzneim. 3 Bd. p. 110). The general effects arevery similar on all classes, and consist essentially of loss of sensation andvoluntary motion, with convulsive movements. The cold-blooded animalsare more slowly affected by it than the hot-blooded ones.

Dr. Christison states that twenty-five grains of the strong acid, appliedto the mouth, killed a rabbit within ten seconds. I once caused theinstantaneous death of a rabbit by applying its nose to a receiver filledwith the vapour of the pure acid: the animal was killed without theleast struggle. If a drop of the pure acid be placed on the throat of adog, or applied to the eye, death takes place in a few seconds. Inhalingthe vapour decidedly produces death more quickly than any other modeof applying the acid.

(c.) On man. —a. In small or medicinal doses. —Small doses of hydro-cyanic acid sometimes relieve certain morbid conditions (as of thestomach), without producing any remarkable alteration in the conditionof the general system. If the dose be cautiously increased, and itsoperation carefully watched, the following effects are usually observed :bitter but peculiar taste; increased secretion of saliva; irritation in thethroat; frequently nausea; disordered and laborious respiration (some-times quick, at others slow and deep); pain in the head, giddiness,obscured vision, and sleepiness. The vascular system is in some casesnot obviously affected, but in others much affected, though not uniformly;being sometimes quickened, at others reduced in frequency. In someinstances faintness is experienced. Drs. Macleod and Granville ( LondonMed. and Physic . Journ. vol. xlvi. pp. 359 and 363) have noticed saliva-tion and ulceration of the mouth during its medicinal use.

ji. In poisonous doses: convulsions and insensibility: if death occur, ittakes place slowly. —Immediately after swallowing the acid, a remarkablybitter taste is experienced; this is soon followed by a sensation of faint-ness and giddiness, with salivation, and succeeded by tetanic convulsions,and insensibility ; the respiration is difficult and spasmodic ; the odourof hydrocyanic acid may be recognized in the breath; the pupils areusually dilated, though sometimes contracted; the pulse is small orimperceptible. When recovery takes place it is usually very rapid, andthe whole period of suffering seldom exceeds half an hour. However,exceptions, to this exist, in which the symptoms have been prolonged forseveral hours.

The following case, related by Dr. Geoghegan, ( Dublin Med. Journ.Nov. 1835), is an interesting illustration of these effects :—A gentleman,aged 21, having been for some time subject to an uneasiness in the sto-mach, not actually amounting to gastrodynia, after having tried many