CHALK-STONES, in Medicine, signify the concretions of calcareous matter in the hands and feet of people violently afflicted with the gout. Leeuwenhoek has been at the pains of examining these by the microscope. He divides them into three parts. The first is composed of various small parcels of matter looking like white grains of sand; this is harder and drier, and also whiter, than the rest. When examined with large magnifiers, those are found to be composed of oblong particles laid closely and evenly together: though the whole small stones are opaque, these component parts of them are pellucid, and resemble pieces of horse-hair cut short, only that they are somewhat pointed at both ends. These are so extremely thin, that Mr Leeuwenhoek computes that 1000 of them placed together would not amount to the size of one hair of our heads. The whole stones in this harder part of the chalk are not composed of these particles, but there are confusedly thrown in among them some broken parts of other substances, and in a few places some globules of blood and small remains of other juices. The second kind of chalky matter is less hard and less white than the former, and is composed of fragments or irregular parts of those oblong bodies which compose the first or hardest kind, and these are mixed among tough and clear matter, and interspersed with the small broken globules of blood discoverable in the former, but in much greater quantity. The third kind appears red to the naked eye; and, when examined with glasses, is found to be a more tough and clammy white matter, in which a great number of globules of blood are interspersed; these give it the red appearance it has.