_b._ Provided picrotoxine has not been found, the _ethereal solution_ obtained by agitating the alkaline fluid with ether is to be examined for colchicine and digitaline. To this end, the residue obtained upon evaporating the solution to dryness is taken up with water, and the filtered fluid tested as follows: 1. It is ascertained if a drop of the solution possesses the bitter taste of digitaline. 2. Another drop is treated with solution of tannin; if either alkaloid be present, a precipitate is formed. 3. Two drops of the solution are next tested: one with tincture of iodine, the other with chloride of gold. These reagents precipitate colchicine, but do not affect solutions of digitaline or picrotoxine. Unfortunately traces of atropine, possibly present, would cause the same reaction; the test therefore fails to be conclusive. 4. Several portions of the solution are evaporated on watch crystals. Concentrated nitric acid is added to one portion: if colchicine be present, an evanescent violet coloration is produced, which changes to a light yellow upon addition of water, and to a pure yellow or reddish-orange color, if the mixture is saturated with a slight excess of caustic alkali. 5. Another portion of the residue is dissolved in a few drops of concentrated sulphuric acid, and the solution stirred with a glass rod moistened with bromine water: in presence of digitaline a violet-red color is produced. This coloration is more distinct when a small quantity of the alkaloid and an excess of sulphuric acid are present. 6. If a large amount of substance is at hand, the residue can be boiled with hydrochloric acid, and the green or brownish color and characteristic odor of digitaline produced, in case this body be present: this, however, is not a very delicate test. 7. Finally; it is advisable when the presence of digitaline is suspected to ascertain its physiological action. For this purpose, a minute quantity of the substance is placed upon the heart of a frog: in presence of the alkaloid, the pulsations are immediately retarded, or even arrested. * * * * * Although by means of the tests given above the existence of a special alkaloid, or of one of the ill-defined substances just mentioned, may be justly regarded as probable, its presence has not yet with certainty been demonstrated. This is especially true in cases where the compound possesses but few characteristic properties. When possible, the suspected substance should be obtained in a crystaline form, and then compared by aid of the microscope--if the small quantity present permits of no other examination--with crystals of the pure alkaloid, prepared under the same conditions.