Physiologically, alkaloids as a class have a powerful action on the human and animal frame. The medicinal properties of plants are generally due to these substances, though many are still undiscovered or imperfectly known. They exist in the plant combined with vegetal acids, some of which are characteristic, as aconitic acid in aconite, meconic in opium, igasuric (?) in nux vomica, &c. The very small quantity which may sometimes be fatal (a fraction of a grain of the pure alkaloid), the indefiniteness of many of their chemical reactions, and the facility with which they decompose if too high a heat, or too strong reagents, be employed in their extraction, render the detection often a difficult, and sometimes an impossible matter. Fortunately, however, fresh tests and better processes develop from every case, and other indications, from symptoms and collateral circumstances, rarely fail to bring home the guilt even to the most ingenious and scientific of poisoners. For extracting the alkaloids from animal matters the following process has been used by the author. Mince finely, digest with rectified spirit and enough acetic acid to _just acidify_, warm to blood-heat for 15 minutes, filter: this is the first extract. Warm the insoluble matters with more alcohol and filter again: this is the second extract. Repeat the extraction a third time. _Keep the three extracts separate._ Each should be evaporated at as low a temperature as possible, not exceeding 50° C., and preferably in a vacuum at the ordinary temperature, if this can be done fairly quickly. The syrupy residues must be treated with water and a drop of acetic acid, passed through wet filters to separate fat, rendered just alkaline with ammonia, and shaken with a moderate quantity of a mixture of equal volumes of ether and chloroform (Allen). By a stoppered funnel or burette the ethereal layer is separated, the shaking with ether and chloroform and the separation repeated a second and a third time, the ethereal extracts mixed, transferred to a large porcelain dish, and evaporated, first in a current of air, then in a vacuum or spontaneously. As the solvents evaporate, water generally appears: this hinders any crystallization. Therefore the residue must be rendered _dry_, then dissolved in a little _anhydrous_ chloroform (dried by standing over fused calcium chloride), and again evaporated in air in a large watch glass. The residue will generally be crystalline under the microscope if any alkaloid be present. Dissolve again in chloroform, transfer to a graduated burette, make up to a convenient volume (say 10 cubic centimetres), and transfer a measured fraction to a number of watch glasses, reserving about one-fourth for any subsequent _quantitative_ test that may be necessary. Allow the liquid in the watch glasses to spontaneously evaporate. To the first add a little water and a very minute quantity of dilute hydrochloric acid, and cautiously taste a portion. A tingling of the lips and