The physical examination, say of the contents of the stomach and intestines, should commence with noting the smell, color, and general appearance of the matters submitted for examination. The odor, for instance, may be useful in indicating the presence of prussic acid, of alcohol, of opium, or of phosphorus. The color may indicate the presence of salts of copper, of fragments of cantharides, &c. The general appearance may give some clue to the mode of introducing the poison, the kind of food or drink used to conceal it, &c. Seeds of poisonous plants may be found: this is especially the case in India, where the seeds of datura are frequently used for criminal purposes; or the poisonous substance may have been administered in such quantity that a portion of it may at once be secured for analysis. This not unfrequently happens in poisoning by arsenic. It is not enough to employ the naked eye in examining these suspected matters; a hand lens of some power should be used; in this way characteristic crystalline forms, botanical peculiarities, and such like, may be made out. Still these are merely introductory to the most important part of the research, which ought to be undertaken systematically, especially if the quantity of material to be operated on is small. Most frequently the matters to be examined are mixed, some soluble, some insoluble; but there may also be submitted for analysis portions of the pure substance. The object of the analyst is to obtain the substances which he has to examine chemically in as pure a condition as possible, so that there may be no doubt about the results of his testing; also, of course, to separate active substances from those that are inert, all being mixed together in the stomach and alimentary canal. Again, in dealing with such fluids as the blood, or the tissues of the body, their natural constituents must be got rid of before the foreign and poisonous body can be reached. There is this difficulty further to contend with: that some of the most poisonous of substances are of unstable composition and readily altered by chemical reagents; to this group belong many vegetable and most animal poisons. These, therefore, must be treated differently from the more stable inorganic compounds. With an inorganic poison we may destroy all organic materials mixed with it, trusting to find it still recognizable after the process; not so with an organic substance: that must be separated by other than destructive means.