CHAPTER XII
IDENTIFICATION OF HUMAN BLOOD AND HUMAN HAIR
Structure of Blood—Human Blood—Blood of Animals—Blood Crystals—Libellers of Sir E. Godfrey—Trial of Nation in 1857—Physiological Tests—Precipitines—First Trial in France—Gorse Hall Trials—Human Hair—Hairs of Animals.
In its structure blood may be described as a colourless fluid, the plasma having in suspension small solid substances—the red and white corpuscles. The plasma may be separated into a coagulated body termed fibrin and a transparent liquid called the serum. When blood coagulates, or forms clots, it forms a solid mass in which the red corpuscles are bound up in the fibrous mass of fibrin. The process of coagulation is promoted by moderate heat, slight dilution with water, and exposure to the air, while it is retarded by cold, strongly heating, great dilution and the addition of various chemical agents.
The red corpuscles differ in size and shape according to the species of animal. Thus in human blood and in the blood of most mammalia they appear as double concave circular discs, while in the blood of the camel and in that of birds, reptiles and fish the red corpuscles are elliptical in form.
The number of corpuscles present is also subject to great variations, the blood of amphibia and reptiles, for instance, containing remarkably few. The following numbers in 100 parts of the blood of different animals have been recorded: Horse, 53; pig, 43·5; ox, 35; dog, 35·7; and man, 48 corpuscles.
The colour of blood is due to a compound known as hæmoglobin, which constitutes about 40 per cent. of the substance of the corpuscles. In the bright red arterial blood the hæmoglobin is present in the form of oxyhæmoglobin, and the latter may be separated in crystalline form by suitable treatment of the separated red blood corpuscles. These crystals differ in the case of different animals both in their chemical and physical characteristics, and have very different forms.
There are also similarly pronounced differences between the microscopical appearance of oxyhæmoglobin crystals from human blood and from that of various animals. The crystals from human blood are in the form of long rhombic needles; those from the blood of the horse are quadrilateral prisms; the blood of the guinea-pig, rat, and many birds yield rhombic tetrahedea; while that of the squirrel gives hexagonal plates.
Crystals of other compounds of hæmoglobin, such as hæmin, differing in the case of different species of animals may also be prepared, and the identity of oxyhæmoglobin may also be proved by its characteristic appearance in the spectroscope.