In the first place, pointed evidence as to the individual who gave the poison may be derived from the chemical investigation,—for example, from the comparative results of the analysis of the poisoned dish, and of the articles of which it consisted. I am indebted to my colleague, Dr. Alison, for the following excellent illustration from the case of William Muir, who was condemned at Glasgow in 1812 for poisoning his wife. In the course of the day on which she took ill she was visited by a farmer of the neighbourhood, who had studied physic a little in his youth. He learned from her that she had breakfasted on porridge a short time before she felt herself ill, and that she suspected the porridge to have been poisoned. He immediately procured the wooden bowl or _cap_ in which the cottagers of Scotland keep the portion of meal used each time for making the porridge; and finding in it some meal, with shining particles interspersed, he wrapped a sample in paper, and took the proper measures for preserving its identity. He then secured also a sample from the family store in a barrel. The two particles were produced by him on the trial; and from experiments made in court the late Dr. Cleghorn was enabled to declare, that the meal from the bowl contained arsenic, and that the meal from the barrel did not. These facts, besides proving that the woman had next to a certainty taken arsenic in the porridge, likewise, in conjunction with other slight moral circumstances, established that the poison had been mixed with the meal in the house, and on the morning when the deceased took ill, before any stranger entered the house. The procedure of this farmer was precisely that which ought to be followed by the medical practitioner in a similar conjuncture. An instance of an opposite description related by M. Barruel also deserves notice, as showing how evidence of this kind may afford, in otherwise suspicious circumstances, a strong presumption of accidental poisoning. Sixteen people near Bressières in France having been severely affected with vomiting and colic immediately after dinner, the bread, which was suspected, was examined by Barruel, and found to contain a little arsenic. The flour of which the bread was made had been taken from a large store of it, which, on being examined, was also found to be similarly impregnated. As it was extremely improbable that any one either could or would poison so large a mass of flour, to attain any malicious object, it was inferred that the arsenic had been mixed with it accidentally, and that the accident might have arisen from grain having been taken by mistake to the flour-mill to be ground, which had been intended originally for seed, and sprinkled with arsenic to destroy insects.[121]