The contemporaries and immediate followers of Lavoisier were the first to make a systematic attempt to elucidate the chemical nature of organic products of animal origin. To this period belongs the work of Fourcroy and Vauquelin on animal chemistry. Chevreul, a pupil of Fourcroy worked on urine, adipocire, and the animal fats in the first decade of the last century. Kirchhoff in 1811, discovered the method of converting starch into sugar; and Döbereiner, in 1822, described a method of preparing formic acid artificially. Dumas and Boullay, in 1827–1828, prepared a number of new derivatives of ethyl alcohol; and in 1834 Dumas and Peligot studied in like manner the chemistry of methyl alcohol, and pointed out many analogies which their compounds possessed, not only among themselves, but also to inorganic substances. Although a considerable amount of information as to the existence, modes of occurrence, and properties of bodies found in the animal and vegetable kingdoms had been accumulated by the end of the first quarter of the nineteenth century, no serious attempt was made to study them systematically until after that period. In fact, they were not even regarded as coming within the operations of laws found to be applicable to the products of the inorganic world, by the investigation, of which products, indeed, those laws had been discovered. Down to 1828 it was considered that inorganic and organic substances were sharply differentiated by the circumstance that, whereas the former might be prepared by artificial means, and even built up from their elements by synthetic processes in the laboratory, the latter could only be formed in the bodies of animals and plants as the result of vital force. In that year Wöhler showed that urea, pre-eminently a product of animal metabolism, could be prepared synthetically from inorganic materials. Other instances of a similar kind were discovered in rapid succession; and the idea that organic substances could alone be formed by vital processes was proved to be invalid. Moreover, large numbers of substances of a character analogous to those produced by physiological action, but not known to occur in the animal or vegetable kingdom, were prepared. There is, therefore, no absolute distinction to be drawn between the chemistry of the inorganic and organic worlds.