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CHAPTER V.

Blood-stains-Chemical, Microscopical, Spectroscopical Methods of Investigation-Coagulation of Blood-Conditions Influencing Coag

ulation.

NOT unfrequently, in cases of murder, it becomes necessary to determine if certain dark stains, such as are found on a knife, linen, underwear, pieces of wood, etc., were made by blood. The appearance presented by bloodstains will vary according to their size, shape, and color. Usually the stain consists of distinct spots; it may, however, be a mere streak or film. The color of recent bloodstains is red, that of old ones brown or brownish-red. It will be more or less modified according to the nature of the material upon which the blood has fallen. Thus the color of blood upon soft wood, linen, or cloth is dark; that upon a polished metallic surface is shining, the spots presenting in the latter case cracks radiating from the centre. There are three methods of examining stains supposed to have been made by blood, the chemical, the microscopical, the spectroscopical, all of which, on account of the importance of the subject, merit at least a brief description.

The chemical method of investigation is based upon the fact that the hæmoglobin of the blood is soluble in cold water. If the suspected blood-stain is in sufficient quantity and not so old that the hæmoglobin has been converted into hæmatin, by proper manipulation a solution

of the coloring matter of the blood can be obtained and then tested. If the article stained be a linen shirt, for example, a small piece should be cut out and suspended in a test-tube containing cold distilled water. In a few minutes, or longer, if the stain be an old one, the coloring matter of the blood will pass into the water, coloring it red. If the stained material to be examined is attached to wood or a knife-blade, it must be scraped or cut off and then soaked in water. Should the solution be not complete, a trace of citric acid or a little ammonia may be added, the latter not affecting the color of the solution. The solution so obtained should then be heated in a test-tube over a spirit-lamp. If the solution be that of the coloring matter of the blood, it will coagulate, the red color will disappear, and a brownishgreen material will be precipitated. In this way a solution of the coloring matter of the blood may usually be distinguished from other red solutions, such as those of red prints, logwood, kino, madder, cochineal, which do not coagulate when heated, and which change their color when ammonia is added.

Stains made by red paint or by lemon-juice on iron, while slightly resembling blood-stains, can be distinguished from the latter through their color becoming a bluish, inky black on addition of tincture of galls, ferro-cyanide of potassium, or by other tests for iron. Another test for blood, that known as the guaiacum test, is based upon the fact that the resin of guaiacum when oxidized assumes a sapphire-blue color, and that this change in the color of the resin can be induced by the addition of blood and peroxide of hydrogen together, but not by the addition of blood alone. A convenient way of applying the guaiacum

test, frequently made use of by the writer, is to add a few drops of a freshly-prepared tincture of guaiacum to a small quantity of water, by which the resin is precipitated. The water holding the resin in suspension is then divided into three portions. To the first portion a few drops of peroxide of hydrogen dissolved in ether are added; to the second portion a few drops of the solution supposed to contain the coloring matter of the blood. In neither case will any change in the color of the resin be observed. Now to the third portion add a few drops of the suspected solution and of the etherized peroxide, and at once the resin will assume a sapphire-blue color. Should the solution be turbid through excess of the resin, a few drops of alcohol will instantly clear it. It should be mentioned in this connection that the resin of guaiacum in the presence of peroxide of hydrogen is oxidized, turns blue by the addition of bile, saliva, red wine, as well as by blood. The color of bile and saliva, however, should serve to distinguish these secretions from blood, while in the case of red wine several hours are required to produce the blue color in the resin. It will be observed that the existence of blood is not directly proved by the chemical tests just described, but is inferred from the presence of its coloring matter or hæmoglobin, and in most cases is only presumptively established.

The microscopic method of proving the existence of blood depends on the ability of the examiner to treat the material submitted to him in such a way that if it be blood the corpuscles, and more especially the red ones, may be sufficiently restored to admit of identification under the microscope, or at least to enable him to obtain the crystalline forms developed through changes in their coloring matter. The separation of the corpuscles from a

material consisting of pieces of linen, wood, or iron stained with blood mixed with dirt, etc., is a far more difficult operation, however, than that of demonstrating simply the presence of blood-crystals. If the material submitted for examination is a piece of linen, for example, stained with what is supposed to be blood, a piece of it should be cut out and placed upon a clean glass slide and moistened with

FIG. 13.

Blood-Corpuscles (450).

a solution consisting of one part of glycerine to seven of water, or with a solution of common salt having a specific gravity of that of the serum of the blood. The specimen should then be covered with a thin cover-glass and examined with the microscope. By this method, if the stain be blood, and not too old, the red blood-corpuscles and sometimes the white ones as well will be usually brought into view. If the material suspected to be blood is in the form of a clot, on a knife-blade, for example, a small portion of it should be scraped off with a needle on to a perfectly clean glass slide. A thin cover-glass being pressed firmly down on the fragment until it is reduced to powder, the glass slide is then placed upon the stage of the microscope. A drop of distilled water being allowed to flow slowly from the margin of the cover-glass toward the powdered material, if the latter be blood the corpuscles will gradually make their appearance, and, although faint and colorless,

are usually sufficiently definite in outline to admit of identification.

A red blood-corpuscle of man (Fig. 13), as seen in freshly-drawn blood, may be described as a biconcave disk, a mass or cell of protoplasm without a cell wall or nucleus, and with a diameter in its greatest width on an average of 20th of an inch.

Micrometer.-Inasmuch as there are obtained from supposed blood-stains certain bodies having the size just mentioned, and as this is usually regarded as one of the strongest proofs that such bodies are red blood-corpuscles, the method by which they are measured must be described. The instrument used for this purpose by the microscopist is an eye-piece micrometer, that is, an eye-piece upon the glass of which have been ruled a number of parallel and equidistant lines, which, on being projected upon the field of the microscope, will be seen by the observer to cover any objects visible there and to define their limits. To use the eye-piece micrometer, the value of the spaces between the lines must be determined for the particular magnification, since these will vary with the objective and the length of tube used. To accomplish this, there is placed upon the stage of the microscope a glass slide upon which have been ruled a number of parallel lines separated from one another by distances of

th,

th, and 10th of an inch respectively (Fig. 14). Let us suppose, for example, that the magnifying power used is such that ten lines of the eye-piece micrometer correspond exactly to the space between two of the lines upon the stage micrometer that are separated byth of an inch, the value of the spaces between the lines of the eyepiece micrometer will be then equal to Tobooth of an inch, and an object covered by four such spaces as a white

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