_Apollodorus_ lived at the commencement of the third century B.C.: he wrote a work on poisonous animals, and one on deleterious medicines; these works of Apollodorus were the sources from which Pliny, Heraclitus, and several of the later writers derived most of their knowledge of poisons. _Dioscorides_ (40-90 A.D.) well detailed the effects of cantharides, sulphate of copper, mercury, lead, and arsenic. By arsenic he would appear sometimes to mean the sulphides, sometimes the white oxide. Dioscorides divided poisons, according to their origin, into three classes, viz.:-- 1. =Animal Poisons.=--Under this head were classed cantharides and allied beetles, toads, salamanders, poisonous snakes, a particular variety of honey, and the blood of the ox, probably the latter in a putrid state. He also speaks of the “_sea-hare_.” The sea-hare was considered by the ancients very poisonous, and Domitian is said to have murdered Titus with it. It is supposed by naturalists to have been one of the genus _Aplysia_, among the _gasteropods_. Both Pliny and Dioscorides depict the animal as something very formidable: it was not to be looked at, far less touched. The aplysiæ exhale a very nauseous and fœtid odour when they are approached: the best known of the species resembles, when in a state of repose, a mass of unformed flesh; when in motion, it is like a common slug; its colour is reddish-brown; it has four horns on its head; and the eyes, which are very small, are situated between the two hinder ones. This aplysia has an ink reservoir, like the sepia, and ejects it in order to escape from its enemies; it inhabits the muddy bottom of the water, and lives on small crabs, mollusca, &c. 2. =Poisons from Plants.=--Dioscorides enumerates opium, black and white hyoscyamus (especially recognising the activity of the seeds), mandragora, which was probably a mixture of various solanaceæ, conium (used to poison the condemned by the people of Athens and the dwellers of ancient Massilia), elaterin, and the juices of a species of euphorbia and apocyneæ. He also makes a special mention of aconite, the name of which is derived from _Akon_, a small city in Heraclea. The Greeks were well aware of the deadly nature of aconite, and gave to it a mythical origin, from the foam of the dog Cerberus. Colchicum was also known to Dioscorides: its first use was ascribed to Medea. Veratrum album and nigrum were famous medicines of the Romans, and a constituent of their “_rat and mice powders_;” they were also used as insecticides. According to Pliny, the Gauls dipped their arrows in a preparation of veratrum.[2] Daphne mezereon, called by the Romans also smilax and taxus, appears to have been used by Cativolcus, the king of the Eburones, for the purpose of suicide, or possibly by “taxus” the yew-tree is meant.[3] [2] Pliny, xxv. 5. [3] _De Bello Gallico_, vi. 31.