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 from some other cause, "extract, or draw out the same, and thus cure the patient." The metals used were combinations of copper, zinc, and gold; or of iron, silver, and platinum. The tractors were invented by Elisha Perkins, the father of Benjamin, who died at New York in 1799. The tractors were united together like a pair of compasses, and one of the arms was obtuse and the other pointed. They professed to apply galvanic action to the relief and cure of pain and disease. Galvani's report of his experiments was only published about 1790, and not much earlier Mesmer's animal magnetism had excited marvellous interest in Paris. Perkins's Tractors had an enormous popularity for a time in England and in Denmark, but nowhere else to any extent. Two Bath doctors, named Falconer and Haygarth, professed to get as good results with tractors made of wood, many patients of the Bath Hospital declaring that these promptly relieved their pains. From these experiments it was argued that the alleged cures were entirely due to the imagination of the sufferers.

After 1800 medicinal compounds are only rarely patented. Of those known to the present generation, Ford's Balsam of Horehound appears in 1816, Savory's Seidlitz Powders were protected in 1815, Ridge's Food, 1862, and Page Woodcock's Wind Pills, 1852. A patent was taken in 1853 by Sir James Murray for aerating cod-*liver oil with carbonic acid gas, and William Brockedon's patent for compressing drugs and blacklead, which has borne fruit a thousandfold in these later days, was granted in 1843.