§ 9. From the treatise of Barthélémy d’Anglais[17] in the thirteenth century (in which he noticed the poisonous properties of quicksilver vapour), up to the end of the fifteenth century, there are numerous treatises upon poison, most of which are mere learned compilations, and scarcely repay perusal. In the sixteenth century, there are a few works, such, for example, as Porta, which partook of the general advancement of science, and left behind the stereotyped doctrine of the old classical schools.[18]
[18] In the sixteenth century it was not considered proper to write upon poisons. Jerome Cardan declared a poisoner worse than a brigand, “and that is why I have refused not only to teach or experiment on such things, but even to know them.”--_J. Cardan: De Subtilitate_. Basel, 1558.
In the seventeenth century the Honourable Robert Boyle made some shrewd observations, bearing on toxicology, in his work on “The usefulness of Natural Philosophy,” &c.: Oxford, 1664. Nicolas L’Emery also wrote a _Cours de Chimie_,--quite an epitome of the chemical science of the time.[19]
[19] _Cours de Chimie, contenant la manière de faire les opérations qui sont en usage dans la Médecine._ Paris, 1675.
In the eighteenth century still further advances were made. Richard Mead published his ingenious _Mechanical Theory of Poisons_. Great chemists arose--Stahl, Marggraf, Brandt, Bergmann, Scheele, Berthollet, Priestley, and lastly, Lavoisier--and chemistry, as a science, was born. Of the chemists quoted, Scheele, in relation to toxicology, stands chief. It was Scheele who discovered prussic acid,[20] without, however, noting its poisonous properties; the same chemist separated oxalic acid from sorrel,[21] and made the important discovery that arsenic united with hydrogen, forming a fœtid gas, and, moreover, that this gas could be decomposed by heat.[22] From this observation, a delicate test for arsenic was afterwards elaborated, which for the first time rendered the most tasteless and easily administered poison in the whole world at once the easiest of detection. The further history of what is now called “Marsh’s Test” is as follows:--
[20] _Opuscula Chemica_, vol. ii. pp. 148-174.
[21] _De Terra Rhubarbi et Acido Acetosellæ._ _Nova Acta Acad. Veg. Sued. Anni_, 1784. _Opuscula Chemica_, vol. ii. pp. 187-195.