Arsenic, 331 Phosphorus, 301 Preparations of Copper, 183 The Mineral Acids, 54 Cantharides, 35 Strychnine, 14 Opiates, 12 Mercurial preparations, 9 Antimonial preparations, 6 Cyanides (that is, Prussic Acid and Potassic Cyanide), 5 Preparations of Iron, 5 This list accounts for 955 poisonings, and the remaining 45 will be distributed among the less used drugs and chemicals. IV.--The Connection between Toxic Action and Chemical Composition. § 23. Considerable advance has been made of late years in the study of the connection which exists between the chemical structure of the molecule of organic substances and physiological effect. The results obtained, though important, are as yet too fragmentary to justify any great generalisation; the problem is a complicated one, and as Lauder Brunton justly observes:-- “The physiological action of a drug does not depend entirely on its chemical composition nor yet on its chemical structure, so far as that can be indicated even by graphic formula, but upon conditions of solubility, instability, and molecular relations, which we may hope to discover in the future, but with which we are as yet imperfectly acquainted.”[32] [32] _Introduction to Modern Therapeutics_, Lond., 1892. 136. The occurrence of hydroxyl, whether the substance belong to the simpler chain carbon series or to the aromatic carbon compounds, appears to usually endow the substance with more or less active and frequently poisonous properties, as, for example, in the alcohols, and as in hydroxylamine. It is also found that among the aromatic bodies the toxic action is likely to increase with the number of hydroxyls: thus phenol has one hydroxyl, resorcin two, and phloroglucin three; and the toxic power is strictly in the same order, for, of the three, phenol is least and phloroglucin most poisonous. Replacing hydrogen by a halogen, especially by chlorine, in the fatty acids mostly produces substances of narcotic properties, as, for instance, monochloracetic acid. In the sulphur compounds, the entrance of chlorine modifies the physiological action and intensifies toxicity: thus ethyl sulphide (C₂H₅)₂S is a weak poison, monochlorethyl sulphide C₂H₅C₂H₄ClS a strong poison, and dichlorethyl sulphide C₄H₈Cl₂S a very strong poison: the vapour kills rabbits within a short time, and a trace of the oil applied to the ear produces intense inflammation of both the eyes and the ear.[33] [33] V. Meyer, _Ber. d. Chem. Ges._, XX., 1725.