18. Of Genital Organs.—Incised wounds of penis may produce fatal hæmorrhage. Removal of testicles may prove fatal from shock to nervous system. Wounds of the spermatic cord may be dangerous from hæmorrhage. Wounds to the vulva are dangerous, owing to hæmorrhage from the large plexus of veins without valves.
XV.—DETECTION OF BLOOD-STAINS, ETC.
Stains may require detection on clothing, on cutting instruments, on floors and furniture, etc. The following are the distinctive characters of blood-stains:
(a) Ocular Inspection.—Blood-stains on dark-coloured materials, which in daylight might be easily overlooked, may be readily detected by the use of artificial light, as that of a candle, brought near the cloth. Blood-spots when recent are of a bright red colour if arterial, of a purple hue if venous, the latter becoming brighter on exposure to the air. After a few hours blood-stains assume a reddish-brown or chocolate tint, which they maintain for years. This change is due to the conversion of hæmoglobin into methæmoglobin, and finally into hæmatin. The change of colour in warm weather usually occurs in less than twenty-four hours. The colour is determined, not entirely by the age of the stain, but is influenced by the presence or absence of impurities in the air, such as the vapours of sulphurous, sulphuric, and hydrochloric acids. If recent, a jelly-like material may be seen by the aid of a magnifying-glass lying between the fibres. If old, a cinnabar-red streak is seen on drawing a needle across the stain.
(b) Microscopic Demonstration.—With the aid of the microscope, blood may be detected by the presence of the characteristic blood-corpuscles. The human blood-corpuscle is a non-nucleated, biconcave disc, having a diameter of about 1/3500 of an inch. All mammalian red corpuscles have the same shape, except those of the camel, which are oval. The corpuscles of birds, fishes, reptiles, and amphibians, are oval and nucleated. The corpuscles of most mammals are smaller than those of man, but the size of a corpuscle is affected by various circumstances, such as drying or moisture, so that the medical witness is rarely justified in going farther than stating whether the stain is that of the blood of a mammal or not. Unfortunately, the corpuscles are usually so dried that little information regarding their size can be given.
(c) Action of Water.—Water has a solvent action on blood, fresh stains rapidly dissolving when the material on which they occur is placed in cold distilled water, forming a bright red solution. The hæmatin of old stains dissolves very slowly, so employ a weak solution of ammonia, and this will give a solution of alkaline hæmatin. Rust is not soluble in water.
(d) Action of Heat.—Blood-stains on knives may be removed by heating the metal, when the blood will peel off, at once distinguishing it from rust. Should the blood-stain on the metal be long exposed to the air, rust may be mixed with the blood, when the test will fail. The solution obtained in water is coagulated by heat, the colour entirely destroyed, and a flocculent muddy-brown precipitate formed.
(e) Action of Caustic Potash.—The solution of blood obtained in water is boiled, when a coagulum is formed soluble in hot caustic potash, the solution formed being greenish by transmitted and red by reflected light.
(f) Action of Nitric Acid.—Nitric acid added to a watery solution produces a whitish-grey precipitate.