2. =Evidence from= _Post-mortem_ =Appearances=.--The morbid appearances found in cases of poisoning will be treated more in detail when each poison, or group of poisons, comes to be separately considered. A caution may be given here against allowing the _post-mortem_ signs of disease or external injury to exclude the idea of poisoning; for death may to all appearance be the result of disease or injury, and yet be caused by poison. An attention to the _post-mortem_ appearances is important in all cases; for in many instances, where the symptoms were unknown to the experts at the time the inspection was made, they were subsequently found to correspond with the morbid changes which the autopsy revealed. The normal appearance of the stomach is white or nearly so, except during digestion, when it is reddened; yet we may sometimes come across cases in which the mucous membrane of this organ may be found so reddened as to lead to a suspicion of poisoning. The knowledge of this fact, and the absence of symptoms, will prevent an error in diagnosis. Ulceration from disease and from irritant poisoning must be distinguished. In that due to disease, the ulcers formed are, as a rule, small and circumscribed; in those from poison, there is diffused inflammatory redness over other parts of the stomach, and even in the intestines; and the poison, as in the case of arsenic, may be found adhering to the sides of the ulcer. Ulceration is more frequently the result of disease than of the action of poisons. Perforation of the stomach or intestines may be due to ulceration or to corrosion. The condition of the mouth and gullet will help the diagnosis. The appearance of the ulcer and the parts around it, together with the hints just given, must guide the diagnosis. Of _post-mortem_ softening little need be said, beyond stating that it very rarely occurs, and is of course not preceded by symptoms. (For the diagnosis between inflammatory redness of the intestines and _post-mortem_ staining, see page 45.) 3. =Evidence from Chemical Analysis.=--The objects of a chemical analysis are to determine: (1) The presence and nature of the poison. (2) The proportion or quantity of the poison taken. (3) The solution of certain questions connected with the administration of the poison.