92 MEDICAL JURISPRUDENCE Several solvents have been recommended to dissolve out the blood stain for extraction of the red blood corpuscles for microscopic examination but the best for this purpose is Vibert's fluid, which is obtained by mixing two grammes of sodium chloride and half a gramme of mercuric chloride in a hundred cubic centimetres of distilled water. A small piece of the stain should be cut out and soaked in a watch glass with 2 or 3 drops of Vibert's fluid for half an hour. It should then be teased out with needles and examined under the high power. In the absence of Viberts' fluid, normal saline serves the purpose fairly well. Some clots of blood or stains on a dyed cloth are not easily dissolved by these solvents. In such cases a dilute soluiioii_of ammonia will give much better results. Stains on leather or some kinds of wood containing tannic acid are not acted upon by any of these solvents and a two per cent solution of hydrochloric acid is required for effecting the right amount of softening for proper microscopic examination. In the case of stains on a rusty weapon, stone, plaster, mud or earth, they should be scraped with a knife and dissolved in a watch glass or test tube for examination. When investigating blood stains on a knife it often happens that there are no stains on the blade or on the handle but only in the joint. It is, therefore, necessary in such a case to dismantle the parts of the knife for finding out the suspected stain. The blood stain is generally found inside the groove in the handle of the knife and not on its blade which is 'washed carefully by the assailant. A drop of the blood stain solution thus obtained, placed on a slide and viewed under the microscope, may reveal the presence of the red blood corpuscles which are circular, biconcave, non-nucleated discs in all mammalia except camels, in which the red blood corpuscles are oval, biconvex and I non-nucleated. In birds, fishes, amphibia and reptiles, they are oval, biconvex and nucleated. These corpuscles can only be detected and identified by one with considerable experience in microscopy and micrometry, and that too only when a stain is quite fresh, say, about twenty-four hours old, and when a small fragment of a clot is available. In old stains specially on a cloth the red blood corpuscles become shrunken, disintegrated and unrecognizable, especially during the hot weather in India. It is impossible to decide by the microscopic examination of the stain if the blood is of human origin for which the serological test is to be sought for. But in fresh cases it is possible to state that the stain is of mammalian blood. In special cases some information may be obtained by the micro- scopic examination of the stain which may be of immense corroborative value; for instance, in a case of murder in Calcutta, Bose found microfilaria in the stains on the assailant's shirt as well as in the victim's blood.17 Teichmann's Test or Haemin Crystal Test.—A small crystal of sodium chloride and two or three drops of glacial acetic acid are placed on a minute fragment of the stain on a glass slide. A cover slip is applied and the acid is evaporated by gently heating over a small flame. It is allowed to cool and examined under the high power of a microscope. Dark brown rhombic crystals of hsemin or hsematin chloride, arranged singly or in clusters, are seen, if blood is present. Similar crystals may be obtained from indigo-dyed fabrics not stained with blood. Hence in a case of doubt a drop of hydrogen peroxide should be added to the crystals which, if of hcematin, will give off bubbles of gas. This test is of academic interest but not of much practical value. It is undoubtedly a delicate test for haemoglobin of blood but is not always success- ful. If the stain is too old, is washed or is changed by chemical agents, the 17. Beng. Chem. Exam. Annual Rep., 1901.