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Our Pharmacopœias and Dispensatories^[110] have cautiously kept pace with the scientific progress of the age; and in tracing them from their origin to the present time^[111] it is gratifying to observe the gradual influence of knowledge in reducing the number of their articles—simplifying the composition of their formulæ—and improving the processes for their preparation.^[112] Chemistry has also been the means of establishing the identity of many bodies which were long considered as specifically different; thus an extensive list of animal substances has been discarded, since it is known that they owe their properties to one and the same common principle, as to gelatine, albumen, carbonate of lime, &c.; so again the fixed alkaline salt produced by the incineration of different vegetables, has been found to be potass, from whatever plant it may have been obtained, with the exception of sea plants, and perhaps some of the Tetradynamia, the former of which yield Soda and the latter Ammonia. Previous to the Pharmacopœia of 1745, every vegetable was supposed to yield a salt essentially different, and therefore a number of alkaline preparations were recommended, each bearing the name of the particular plant from which it had been procured, as salt of Wormwood—salt of Broom,—Salt of Bean-Stalks, &c.