On the non-existence of sugar in the blood of persons labouring under diabetes mellitus. In a letter to Alexander Marcet, M. D. from William Hyde Wollaston; Sec. R. S

Dr. Marcet, having been requested by Dr. Wollaston to examine whether the serous fluid, secreted in consequence of the application of a blister, could be impregnated with prussiate of potash, gave to a young woman five grains of this prussiate, every hour, till she had taken thirteen or fourteen such doses. After the fifth dose, when her urine became blue immediately by addition of sulphate of iron, a blister was applied, and the serum secreted in consequence was collected, whilst her urine still indicated the presence of the prussiate. But in this serum no prussiate could be detected. Dr. Marcet also repeated Dr. Wollaston’s experiment on serum derived directly from the blood, but with this variation, that the blood was drawn by cupping; and he could not discover the presence of any prussiate.