_Fixing and Staining._--A drop of the watery extract of the stain may be placed on a microscope slide and allowed to dry in the air, covered to protect it from dust, and then fixed by heating the slide over a spirit or Bunsen flame or by the use of absolute alcohol. When fixed, the preparation can be stained with eosin and methylene blue, methylene violet, or other nuclear dye. The film may also be fixed and stained with Leishman‘s solution in one procedure, or fixed by heat first and then stained with Leishman. The procedure is the same as for blood, viz. to cover the film with a few drops of Leishman‘s stain, let stand for two or three minutes, then add a few drops of distilled water, in two or three minutes wash in distilled water, dry with filter paper, and examine with the oil immersion. The preparation may be mounted in Canada balsam and preserved for further reference. The head of the spermatazoon takes the nuclear dyes in ordinary use. The spermatazoa are best found in the centre of the stain. If the stain be small the watery extract may be centrifuged. _Florence‘s Reaction._--A useful chemical reaction has been introduced by Dr. Florence of Lyons. It depends upon the reaction between a concentrated solution of iodine in potassium iodide and human semen. A watery extract of the stain is made, and a drop placed on a microscope slide, by Potassium iodide 1.65 grms. Iodine 2.54 “ Distilled water 30 c.c. The drops are covered with a cover glass and examined; where the two drops unite, a precipitate is formed which consists of brown crystals, very similar to hæmin crystals. If there be sufficient material the precipitate may be obtained in a test tube. This test is extremely delicate, and is analogous in value to the guaiacum reaction for blood. A positive reaction does not absolutely prove that the stain is seminal, but a negative reaction proves that it is not. Dr. Florence holds the reaction is specific for human semen, as he has failed to obtain it with the seminal fluid of any other animal, or other fluids or tissues. He considers it due to the presence of an alkaloidal body in human semen, which he calls virispermin. The crystals are said by Dr. Max Richter to form on the addition of the iodine solution to decomposition products of lecithin. The author has found this reaction extremely delicate, even with minute traces. The crystals form rapidly and are easily recognisable. They, however, are evanescent and disappear on standing, so that they cannot be preserved as microscopic specimens.