The Principle of Action Consists of a volatile alkaline Salt, intimately united to, and enveloped in, a corrosive sulphureous Oyl. The Sensations of the Stomach are most evidently exquisite, by Hunger and Thirst; with which those other Senses of Smelling and Tasting are in immediate Contact and Agency, which the wise Ordination of a supream Hand, for the Preservation of Life, has proportionally distributed through every Part of the Creation, from Man down to the most small and apparently insignificant Insect. By the nice Sense of the Palate, we are able to judge in general, what is, and what is not essential to the Nutriment of the Body; which Nutriment the Stomach, for the most Part, rejects when noxious. Some Things, indeed, are almost void of Smell or Taste, therefore not seemingly injurious to the external Senses, and thus may be accidentally taken into the Stomach; or when those Senses are depraved; as Hemlock has been often mistaken, and eat for Parsley; but when a Poison is taken, the nocent Power is put into Action by the internal Heat, and proves a Stimulus on the nervous Coat of the Stomach. "_Porro hujus tunicæ altior in Ventriculum insertio, intimum ac Citissimum illud inter Stomachum & Gulam Commercium_ _facit; ita ut, si pars alter utra in Vomitionem cieatur, mox altera in _σύμπραξιν_ adducatur: cumque eadem tunica, palatum aliasque Oris partes investiat, etiam hæ cum illis circa Vomitionem mutuo consensu afficiuntur. Willis Pharmac. Rationalis_, Sec. 2. Page 5. _Primarum Viarum Descriptio._" Upon this Stimulus, Nature immediately takes the Alarm, and sickens, which Sickness increases with the Vellications, till the offending Power is discharged, or by sudden and violent Inflammation, the Stomach is withheld from discharging the Virus, when the human Mechanism suffers an universal Convulsion. If therefore, by such powerful Efforts of the nervous System, the grosser Parts of the Poison received, cannot be disengaged by proper and timely Assistance, the Nerves lose their Power; the Muscles can no more be brought into Action, but remain in a State of Relaxation, and the whole Body must sink under the Calamity. Thus the Actions of most Poisons, especially the Vegetable, when taken into the Stomach, are nearly the same; all vellicating and inflaming the first Passages, yet the Analysis of them is materially necessary to discover the acting Principles wherewith they are compounded, that we may more exactly point out their separate Cures. Dr. _Mead_ describes the Effects of Poisons in the Primæ Viæ, in so accurate and concise a Manner, that I cannot do better than transcribe his own Words.