2. _Appearance when held to the light._--As uncertain as the preceding. 3. _Doubtful spots upon cotton or linen_--not upon _wool_, which usually contains sulphur--should be cut out and moistened with a few drops of oxide of lead, dissolved in liquor potassæ, and then dried at a temperature of 68° F. The stain in a few minutes becomes of a dirty yellow or sulphur-yellow colour. This change in colour proves that the mark _is not_ a seminal stain. Semen does not contain albumen. This test only shows that the stain is not caused by albuminous compounds, which contain sulphur; but it does not follow therefore that the spot must be seminal, for marks made by gum, dextrine, and some other substances of a like nature are not changed in colour. 4. _The Microscope._--This is by far the most reliable test, but care is required in its manipulation. (_a_) The cloth must not be rubbed between the fingers, as the spermatozoa may be damaged by the operation. (_b_) The suspicious spot on the linen should be carefully cut out and placed in a clean watch-glass or small porcelain vessel, and then moistened with a small quantity of distilled water. The cloth may be gently moved about in the water with a glass rod, and gentle pressure made so as to thoroughly wet the cloth, which, in most cases, will be accomplished in about a quarter of an hour. A single drop should now, by gentle pressure with the fingers, be squeezed on to a clean slide, and then placed under the microscope. (_c_) Another method may be adopted. First determine the side of the cloth on which the stain is present, and cut out the stain, leaving a small strip of cloth attached to the main portion. Place the end of the strip in a little water in a watch-glass, so that the water by capillary attraction may permeate the entire stain. With a thin-bladed knife gently remove the moistened stain and place it on a microscopic slide, and examine as before.