SEMINAL STAINS 107 Fig. 26.—Microphotograph of Choline Periodide Crystals X 500. (Khan Bahadur Dr. IV, J. Vazrfdar.) to this formula. In fact a slightly weaker mixture acts equally or better according to some workers.42 A mixture consisting of 5 per cent of iodine and 8 per cent of potassium iodide in. distilled water is used in our laboratory with satisfactory results. It keeps well for at least three months. The following technique for Florence test has been found quite satis- factory and may be recommended for general application: — The stained portion is snipped off with a pair of scissors and divided into small bits which are soaked in a watch glass with a small amount of water acidulated with hydrochloric acid (about 0.1 per cent solution or one drop of strong hydrochloric acid in 44 cc. of distilled water) for about half an hour. A wet piece is transferred to a slide, is carefully teased with a pair of dissecting needles and is allowed to evaporate almost to dryness. A drop of Florence's reagent is added and a cover glass is placed over the specimen which is then examined under a microscope. If a stain be seminal, dark brown crystals in the form of monoclinic prisms or rhombic plates, often crossed or grouped in clusters, appear imme- diately at the contact of the two solutions and then gradually throughout the specimen. The crystals resemble hseniin crystals in shape, size and colour. In dilute solutions the crystals are smaller and may appear as needles or thin black rods instead of the usual rhombic plates. In scanty stains three, four or more pieces of wet specimens may be taken from the watch glass, teased on a glass slide and then squeezed between the thumb and index finger to obtain as much of the extract as possible. It is then evaporated and pro- ceeded with as before. It is claimed, that this test is extremely delicate, even with minute traces. A negative reaction is conclusive proof that the stain is not seminal, but a positive reaction is merely a preliminary test like the phenolphthalein or 42. UP. Chemical Examiner's Annual Eeport, 1924, p. 3.