Such pattern-forming qualities are found in many fields of nature, very beautifully, for example, as we have seen, in the skin of the zebra; on the back of a mackerel; in the grain of various kinds of wood; in the veining of leaves and petals; and in the covering or substance of seeds such as the nutmeg and scarlet runner bean. Sir Charles Lyell, in his Elements of Geology, figures the ribbing of sand on the sea-shore in a wood-cut which might be an enlarged diagram of human skin. (See fig. on page [32]). In his Principles of Geology (5th ed., vol. i., p. 323) there is, again, a figure described as a section of “spheroidal concretionary Travertine,” which contains many linings strikingly like those with which we have to deal in this little work.
| a. section of pine-wood stem. | b. a human thumb-print. |
It follows from these analogies that a method of analysing and classifying such patterns might have very wide utilities beyond its relation to finger-prints. It is easy, for example, to recognize the same zebra in quite different pictures. Another point of practical importance is this, that a smudgy or blotchy impression, supposed to be that of a criminal present at some seat of crime, might be the impressed copy merely of some object or texture other than human skin, but containing lineations of similar arrangement. An outworn transversely cut branch of a tree might readily produce a print like that of a human finger. An expert would probably notice that in the lineations there were no real junctions, each woody ring remaining apart from the others; but, again, there are some human fingers of such patterns. I think the bloody smear officially reproduced as impressed on a post-card in facsimile, and purporting to have come from “Jack the Ripper,” at the time of the Whitechapel horrors in the eighties, may have been produced by the sleeve of a twilled coat smeared with blood. It contained no characters specially characteristic of skin lineations, which it was presumed to be an example of, as impressed.
Apart from all that, lemurs, lemuroids, apes, anthropoids, and monkeys, all show on hands and feet, skin lineations in patterns similar to those of man. In the anthropoid apes it would not be easy to discriminate them from those of human beings. Some of these were figured in my Guide, and Dr. Otto Schlaginhaufen has supplied numerous good prints.
If Edgar A. Poe, in his famous mystery of evil deeds done by a gigantic ape, had been acquainted with finger-print methods, he might have pictured the police as still more mystified by the imprints of seemingly human hands.
There are two methods of observing systematically the lineation patterns.
1.—The Direct Mode.—This might be done simply by many people by looking at the lineations with the unaided vision. Till quite recently the author found no difficulty in doing this, with myopic eyes that could see something of the texture of a house-fly’s eyes in a good light. My earliest observations of the finger-patterns were made in this way, while the patterns were reproduced in pencilled outlines. The condition of the actual ridges and furrows themselves, with their open and acting or closed and dormant sweat-pores, ought to be familiar to the student of dactylography, who is apt to narrow his vision by the contemplation only of dead impressions made in ink or otherwise. A lens such as botanists use for field work is very useful, and a high power is neither necessary nor very helpful. Drawings of the patterns ought to be made from time to time with coloured or “lead” pencils, and those drawings should be accurately adjusted by the use of rubber and compasses.
2.—The Indirect Method.—This is done by the medium of casts and printed impressions. Casts may be made of clay, putty, sealing-wax, beeswax, gutta-percha, hard paraffin, varnish, half-dry paint, and the like. Printed impressions or dactylographs may be obtained from greasy or sweaty fingers, blood, printer’s ink, or various substitutes for it.
Within this method, again, two very distinct and complementary kinds of results may be obtained, which I have elsewhere described as Positive and Negative. The first or Positive is that, for example, which is used officially for the record of convicted prisoners by printing with ordinary printer’s ink, just as a veined leaf or fern, or a box-wood engraving is printed from. Here the ridges or raised lines appear black on a white ground, while the intervening furrows appear white, as do also the minute pores dotted along the crest of each ridge. (See [frontispiece].)
In the other method, as when the fingers are impressed on a carefully smoked surface of glass, the projecting ridges lift up the carbon of the soot, leaving a white pattern behind, with the sweat-pores forming black punctuations, while the receding furrows leave the black surface untouched. When such impressions have to be used again, as for evidence, they should be carefully varnished, as they are exceedingly liable to be destroyed by the slightest contact.