st of the ha l' ell rate ( fa di 萬 "naan's cryst They are prepared fansted by a mytre of sod. In enloride and facial adin prese sence of Ebed ecloring matter. crystals are easily recog rised under the microscope. and furnish the most conclusive of the chemical tests for blood. To obtain the test from a stain on clothing a small piece of the Stained fabric should be cut out, and laid upon a microscope slide. A minute crystal of sodium chloride is then placed in the centre of the piece of fabric, and FIG. 25. HEMIN CRYSTALS (Magnified sufficient glacial acetic acid 450 diameters) dropped on it to thoroughly rate, it. The acid should be well worked into the piece of fabric by kneading it with the end of a glass rod, and the fabric should then be rolled up on a piece of platinum wire turned at one end so as to grip it; it will now be easy to express a dirty brown fluid from the fabric by pressure with the glass rod, the fluid being manipulated to the middle of the slide, where a thin cover-glass is dropped upon it. The centre of the slide is then passed to and fro over the flame of a bunsen-burner so as to produce active ebullition of the acetic acid under the cover, which should be continued until it has boiled to dryness. The slide is then allowed to cool and examined under a fifth or sixth inch objective. Under the microscope the crystals appear of a brown colour, with a steel blue lustre by reflected light. They mostly take the form of rhombic plates (fig. 25), which occasionally are superimposed so as to form crosses or stars; they vary very much in size, sometimes being large, whilst at other times they are extremely small. For the application of the hæmin test to blood stains mixed with rust on knives and other weapons, see p. 3. SPECTROSCOPICAL EXAMINATION OF BLOOD STAINS The age of a stain is no impediment to the use of the spectroscopic test. Hæmatin, into which the hæmoglobin finally changes, is a very permanent body; it does undergo certain changes by time, but these changes, which are but little understood, are of no practical moment. Sorby states that he was able to discover the hæmatin bands in a stain forty-four years old, and Tidy obtained excellent spectra from stains which he believed were over a hundred years old. The solution for spectroscopical examination is prepared from the stain by one of the methods described on p. 3. If an alkali be used in the extraction of the stain, the solution obtained will be one of hæmatin, since if the blood colouring-matter has not already undergone that change, alkalies convert hæmoglobin into hæmatin. If the alkaline solution of hæmatin be reduced, the typical spectrum of reduced hæmatin or hæmochromogen, as it is also called, will be obtained. This test is applicable even in cases where no hæmin crystals are obtainable. Struve's process for the extraction of blood stains is to place the portion of stained fabric in a test-tube, cover it with cold water, and allow a stream of carbon dioxide to slowly pass through the liquid. In a period varying from a few minutes to an hour's exposure to the gas, a solution is obtained for spectroscopical examination. If there be sufficient solution, it may be examined in a test Appearance of blood stains-Methods of removing blood stains-Microscopical examination-Spectroscopical examination- Other coloured stains. To say whether suspected spots are blood is frequently a matter that requires great care and experience in spectroscopic and microscopic examinations. The identification of blood stains. not unfrequently furnishes an important link in the chain of evidence in a trial for homicide. It is a common practice when the garments of a suspected murderer are found with red stains on them to attribute the stains to the blood of some domestic animal or bird, or to spots of paint, dye, fruit stains, &c. Appearance of blood stains. Blood stains vary very much. in size, shape, and colour. If the blood has spurted to a distance from a small artery upon the surface of some nonabsorbent object, the spots present a comet-like shape, terminating in a bulbous tail. The upper portion of the spot is VOL. II. B generally of a pale red colour, while to the bulbous extremity the greater portion of the colouring-matter and fibrin has gravitated. Such sprinkling of the blood upon a surface is strongly indicative of its having been ejected from a living body. The colour of a blood stain depends-(i) upon its freshness; if recent, it possesses a bright red colour; if old, the colour is reddish-brown or brownish; (ii) upon its thickness; the thicker a stain the darker its colour; (iii) upon the absorbent nature and colour of the material upon which the blood has fallen; if the material be porous, the colour is dull; if the material be hard and polished, the stains have a shining appearance, provided they are fairly recent. If the stains are on a coloured substance, they are best recognised by artificial light. Before employing any of the tests for blood, a suspected stain should always be examined with a good lens, or with a low power of the microscope. If upon a fabric, the fibres will, in the case of a recent blood stain, present a glossy appearance, and minute clots of blood will be found intermixed with the fibres. If the blood stain be an old one, the fibres will probably appear to be simply stained. Changes that blood stains undergo by time.-If recent, a blood stain is of a red colour, due to hæmoglobin; after a time, which may vary from a very few hours to several days, it assumes a reddish-brown or brownish colour, due to the conversion of the hæmoglobin into methæmoglobin, and finally into hæmatin. These changes of colour are not entirely determined by the age of the stain, but are considerably influenced by the presence or not of impurities in the air. The presence of acid vapours, such as sulphurous, sulphuric, and hydrochloric acids, in the air materially hasten the colourchanges, by effecting the conversion of the hæmoglobin into the brownish acid-hæmatin. This fact is important to bear in mind, as blood stains are liable to change colour much more rapidly in the atmosphere of a manufacturing or other large town than in country air. Hence the conclusion may be drawn, that if the colour of a blood stain be red, the stain is fairly |