Therefore, when it is a question of whether the blood is that of a dog, pig, hare, rabbit, or man, he would be a daring man that would give a decided opinion. But it is certainly possible to come to a safe conclusion as to whether it is that of a human being or a sheep, goat, or elephant.
Owing to the influence of disease on the blood, however, it is never really safe to say absolutely "This is human blood," and, in fact, all that is generally stated in evidence is whether it is mammalian.
There is one other important piece of work the medical detective can perform in his laboratory, in the way of tracking criminals; that is to distinguish hairs from vegetable fibres, and human hairs from animals'. Our illustrations show how it is done. He simply places the thing to be tested under the microscope, and—as he is acquainted with every description of hair, cotton, wool, silk and other fibre—he can tell at a glance what it is.
Hair is more like wool than anything else, but wool is irregular and hair is pretty regular in breadth. The hair of an adult, also, has a streak in the middle.
AN IMPORTANT CLUE—MEASURING FOOTSTEPS.
We append accurate illustrations, from microscopic photographs, of the hairs of many animals. Obviously, there is no difficulty to the practised eye in distinguishing them. In fact, most animals' hairs can be known by the naked eye, or with a small magnifying glass; but that of skye terriers and spaniels is wonderfully like human hair.
On all these little things hinges, very often, the terrible issue of "guilty" or "not guilty"!
Some years ago, a woman was found dead with a knife lying loosely in her hand. This fact might mislead people into thinking it was a case of suicide; but the fact that the knife was not held tight made the doctor suspicious. He examined the blood on the knife, and found woollen fibres which resembled those of the husband's clothes. This discovery so acted on the husband that he confessed his guilt.
On another occasion a Taunton man was seen last in company with a man subsequently found dead. In the Taunton man's possession was a knife with a slight film of blood on the blade. He said he had been cutting raw beef. The analyst easily showed, however, that the blood on the knife came from a living animal; and, further, he found on it some little scales from the lining of the human gullet. The Taunton man was convicted.