GRAVEL AND STONE. All impositions upon this subject may be detected by chemical analysis; in general, it will be sufficient to saw the pretended calculus into two parts, when the absence of the characteristic structure will establish the fraud; it will frequently be found that they are small pebbles, or coarse siliceous sand; _Mr. Wilson_[571] has related two instances of this kind in which an attempt was made to practise on his credulity; “many years ago,” says he, “when I resided in the house of _Mr. Cruikshank_, a person brought his son to that gentleman for surgical advice, asserting that the boy had long been cruelly afflicted with stone; in proof of which he produced several pieces of hard slaty substances, which he stated he had assisted the child in removing from the urethra; upon my expressing an opinion that these were not urinary concretions, he pretended to be angry, and indignantly left the house, declaring that he would seek for a surgeon to perform the operation for the removal of the stone, whose humanity would not let him doubt the assertion of a father, who, though in poverty, would gladly sacrifice his own existence to save that of his son: a few days after this he brought back the boy with a large piece of slate sticking in the urethra, which had torn the inner membrane, and from the swelling it had produced, was with much difficulty removed; wishing to detect the imposture, I persuaded him to leave the boy in _Mr. Cruikshank’s_ house, under the pretence that the operation of lithotomy should be performed, if necessary; and it was only after the forms of binding the boy and bandaging his eyes were gone through, that he could be prevailed upon to confess his father had taught him to introduce these substances, which he had procured from coals, for the purpose of exciting commisseration for his pretended sufferings, and obtaining money from the charitably disposed; and perhaps, in this instance, to have extorted money from the surgeon to conceal his ignorance, had he seriously attempted to perform any operation.”