BLOOD STAINS 93 \ \ Fig. 24 —Microphotograph of Haemin Crystals X 400. (R3. K. N. BagchL) crystals are not formed. The addition of too much salt or presence of mois- ture in the acid or overheating of the slide also results in failure. Hsemochromogen Crystal Test,—This is a delicate and confirmatory test for the presence of hemoglobin. It consists in the addition of two or three drops of Takayama reagent to a small piece of the suspected material on a glass slide in the cold, and covering with a cover slip. Large rhomboidal crystals of a salmon-pink colour and arranged in clusters, sheaves and other forms appear usually within one to six minutes under the low power of a microscope. Occasionally these crystals take longer to form, but slight warming of the slide, especially in cold weather, hastens the reaction. A negative result should not be recorded until after the lapse of half an hour. An important advantage of this test is its adaptability for the spectroscopic test. The same specimen may be examined with the microspectroscope for the spectrum of hsemochromogen. Takayama reagent consists of sodium hydroxide (10 per cent) 3 cc., pyridine 3 cc., saturated solution of glucose 3 cc., and distilled water 7 cc. It should be freshly prepared if prompt action is required. It gives satis- factory results for about two months, if kept in an amber-coloured bottle. Greaves 1S has obtained crystals using the reagent, six months old. Spectroscopical Examination.—The spectroscopical examination is the most delicate and reliable test for determining the presence of blood in both recent and old stains, and is always employed by chemical examiners. A recent blood stain gives a solution of oxyhsemoglobin which, when examined by means of a spectroscope, shows two dark * absorption bands between the Frauenhofer lines, D and E, in the yellow-green in the solar spectrum. The first band is darker and more clearly defined, and lies at wave lengths 587-570, while the second band is lighter and less clearly defined, and lies at wave lengths 550-530. In an old stain oxyhaemoglobin is con- 18. Brit. Med. Jour., May 21, 1932, p. 932.