BLOOD-STAINS. In some criminal trials it is a matter of extreme importance to determine whether certain stains found upon various weap ons. upon clothing. or upon carpets, walls, furni ture, etc., have been made by blood or by sonic other substance. Further, there comes up the question as to whether a blood-stain has been made by human blood or by the blood of one of the lower animals. The appearance of blood stains varies, depending hirgely on the character of the substance stained, age of the stain, etc. As a rule the more permeable the substance, the brighter is the stain. Thus, on cloth the serum is quickly absorbed, leaving a rather bright stain from the colored elements of the blood; while stains on hard surfaces, such as metal and pol ished wood, are usually of a dark color. The question as to whether a given stain is blood is in most cases comparatively easy to answer. The determination may be made by chemical means, by the use of the microscope, or that of the spectroscope. The gualacum test is as follow's: If a drop of blood, or a drop of water with which a blood-stain has been moistened, be placed upon a blotting-paper and a drop of tincture of guaiacum added, the further addition of a drop of hydrogen peroxide will result in the produc tion of a sapphire-blue color. The fact that cer tain substances other than blood may give this or a similar reaction tends to vitiate the value of this test. Another test, known as the Lenin test, is as follows: To a little of the powder scraped from a blood-stain is added a drop of glacial acetic acid with a trace of sodium chlo ride. After standing for sonic time the mixture is
gently heated. As evaporation takes place the specimen should be examined under the micro scope, wh.m numerous rhomboidal crystals will be seen of a reddish, brown, or yellow color. These are produced from the coloring matter of the blood, and arc known as hemin crystals. A positive result from this test is extremely relia ble. On the other hand, a failure to obtain crys tals cannot be (misidered positive proof that the stain is not blood. Very accurate results may be obtained by spectroscopic examination of blood-stains. The fact that hemoglobin (from a fresh stain) and hematin (from an old stain) exist each in two states of oxidation, and that each state has its own characteristic absorption bands in the spectrum, increases the accuracy of this test. The microscope alone is often of value in determining the nature of blood-stains. Thus, if a stain be moistened with a little normal saline solution (sodium chloride 6 per cent. in water), and sonic of the fluid be examined under the microscope, it is often possible, even in the ease of very old stains, to recognize the blood-cor puscles.
The differentiation of the blood of a man from that of a woman or child, or of the blood of one person from that of another, is apparently im possible. The differentiation of a human blood stain from a stain made by blood from one of the lower animals is mentioned in the article BLOOD ) •