Aconitin

Aconitin, the active principle of the aconite or monk's-hood, is one of the most potent poisons known, so small a quantity as $\backslash frac\{1\}\{100\}$th of a grain of the pure alkaloid having nearly proved fatal. Its recognition in poisoning cases is a matter of difficulty, owing to the small amount necessary for the purpose, but there are tests by which it may readily be recognised. It was the drug employed by Dr Lamson in the murder by poison for which he was executed in April 1882. When applied to the eye in even very dilute solution, it causes a sensation of intolerable heat and tingling, the pupil at the same time contracting. This tingling, associated with numbness, is felt when a piece of aconite root is chewed, and on account of this peculiar property, aconitin, or a preparation of aconite, is extensively used in the treatment of neuralgia, rheumatism, and toothache.