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than 54 per cent, of arsenic, is inert, although perfectly soluble. In a paper of great merit, read before the Royal Society last year, we find Dr. A. Crum Brown and Dr. Thomas R. Fraser entering upon this branch of inquiry in a very philosophical spirit. After showing how impossible it is to connect physiological action with composition, they proceed to inquire whether light may not be thrown on the point by taking into consideration the chemical constitution of substances—defining constitution as ‘the mutual relation of the atoms in a substance.’ By an ingenious method of directing experiment, into which I cannot venture to enter here, the authors have arrived at some remarkable results, which may probably at no very remote date give some assistance to the therapeutical student. Whatever may be done, however, by the assistance of chemistry and physiology, we must not underrate the value of the purely empirical method. It is most excellent when carefully applied by persons conversant with disease. The great evil attaching to it is that those who are not competent to determine pathological conditions occasionally addict themselves to therapeutical inquiries. It was thus with Hahnemann, who experimented most
