It has been already stated that we are to a great degree ignorant of the Simples used by the ancient Physicians; we are often quite unable to determine what the plants are of which Dioscorides treats. It does not appear that out of the 700 plants of which his Materia Medica consists, that more than 400 are correctly ascertained; and yet no labour has been spared to clear the subject of its difficulties; Cullen even laments that so much pains should have been bestowed upon so barren an occasion.[76] The early history of botany presents us with such a chaos of nomenclature, that it must have been impossible for the herbarist and physician to have communicated their mutual lights; every one was occupied with disputes upon words and names, and every useful inquiry was suspended, from an inability to decide what plant each author intended; thus, for instance, the _Herba Britannica_ of Dioscorides and Pliny, so celebrated for the cure of the soldiers of Julius Cæsar on the Rhine, of a disease called ‘_Scelotyrbe_’, and supposed to resemble our sea scurvy, remains quite unknown, notwithstanding the labours of our most intelligent commentators.[77] It seems also very doubtful whether the plant which we denominate _Hemlock_ was the poison usually administered at the Athenian executions,[78] and which deprived Socrates and Phocion of life. Pliny informs us that the word _Cicuta_, amongst the ancients, was not indicative of any particular species of plant, but of vegetable poisons in general; this is a circumstance to which I am particularly anxious to fix your attention; it is by no means uncommon to find a word which is used to express general characters, subsequently become the name of a specific substance in which such characters are predominant; and we shall find that some important anomalies in nomenclature may be thus explained. The term ‘Αρσενικον,’ from which the word _Arsenic_ is derived, was an ancient epithet, applied to those natural substances which possessed strong and acrimonious properties, and as the poisonous quality of arsenic was found to be remarkably powerful, the term was especially applied to Orpiment, the form in which this metal more usually occurred. So the term _Verbena_ (quasi _Hebena_) originally denoted _all those_ herbs that were held sacred on account of their being employed in the rites of sacrifice, as we learn from the poets;[79] but as _one_ herb was usually adopted upon these occasions, the word _Verbena_ came to denote that particular herb _only_, and it is transmitted to us to this day under the same title, viz. _Verbena_, or _Vervain_, and indeed until lately it enjoyed the medical reputation which its sacred origin conferred upon it, for it was worn suspended around the neck as an amulet. _Vitriol_, in the original application of the word, denoted _any_ crystalline body with a certain degree of transparency (_Vitrum_); it is hardly necessary to observe that the term