The tests more recently introduced consist in the production of small characteristic crystals, termed _haemin_ crystals, and in the use of the spectroscope. Crystals of haemin (first discovered by _Teichman_) are formed when dry blood is dissolved in concentrated acetic acid, and the solution evaporated to dryness: they are of a brownish-red color. _Brücke_ first suggested an analytical method, based upon this property of blood, which is equally characteristic and sensitive: It is only necessary to dissolve a minute portion of the matter to be examined (dried blood, or the residue left by the evaporation of the fluid obtained by treating the stain, or the dried blood, with cold water) in glacial acetic acid and evaporate the solution to dryness in order to obtain crystals of haemin, which can be readily recognized by means of a microscope having a magnifying power of 300 diameters. If the crystals originate from fresh blood, they appear as represented in Fig. 21; crystals from old blood are represented in Fig. 22. [Illustration: Fig. 21.] [Illustration: Fig. 22.] The former possess a reddish-brown, the latter a lighter color. The various methods now employed to produce haemin crystals were proposed by _Hoppe-Seyler_, by _Brücke_ and by _Erdman_. Whichever process is used, the suspected stains are at first carefully separated from the material upon which they are deposited. If they are present on linen, or other fabrics, the stained portions, which always remain somewhat stiff, are cut off: they will present a reddish-brown color, in case the cloth is not dyed: if the stains are on wood, they are removed by means of a sharp knife; if on stone or iron, they are detached by scraping.