In selecting standard forms of patterns for the convenience of description, we must be content to disregard a great many of the more obvious characteristics. For instance, the size of generally similar patterns in Fig. 10 will be found to vary greatly, but the words large, medium, or small may be applied to any pattern, so there is no necessity to draw a standard outline for each size. Similarly as regards the inwards or outwards slope of patterns, it is needless to print here a separate standard outline for either slope, and equally unnecessary to print outlines in duplicate, with reversed t.i.tles, for the right and left hands respectively. The phrase "a simple spiral" conveys a well-defined general idea, but there are four concrete forms of it (see bottom row of Plate 11, Fig. 17, _oj_, _jo_, _ij_, _ji_) which admit of being verbally distinguished. Again the internal proportions of any pattern, say those of simple spirals, may vary greatly without affecting the fact of their being simple spirals. They may be wide or narrow at their mouths, they may be twisted up into a point (Plate 8, Fig. 14, ~52~), or they may run in broad curls of uniform width (Fig. 14, ~51~, ~54~). Perhaps the best general rule in selecting standard outlines, is to limit them to such as cannot be turned into any other by viewing them in an altered aspect, as upside down or from the back, or by magnifying or deforming them, whether it be through stretching, shrinking, or puckering any part of them. Subject to this general rule and to further and more particular descriptions, the sets (Plates 7 and 8, Figs. 11, 12, 13) will be found to give considerable help in naming the usual patterns.
[Ill.u.s.tration: PLATE 7.
FIG. 11. ARCHES.
FIG. 12. LOOPS.]
[Ill.u.s.tration: PLATE 8.
FIG. 13. WHORLS. CORES TO LOOPS.
FIG. 14. Rods:--their envelopes are indicated by dots. Staples:--their envelopes are indicated by dots. Envelopes whether to Rods or Staples:--here staples only are dotted.
FIG. 15. CORES TO WHORLS.]
It will be observed that they are grouped under the three princ.i.p.al heads of Arches, Loops, and Whorls, and that under each of these heads some a.n.a.logous patterns as ~4~, ~5~, ~7~, ~8~, etc., are introduced and underlined with the word "see" so and so, and thus noted as really belonging to one of the other heads. This is done to indicate the character of the transitional cases that unite respectively the Arches with the Loops, the Arches with the Whorls, and the Loops with the Whorls.
More will follow in respect to these. The "tented arch" (~3~) is extremely rare on the thumb; I do not remember ever to have seen it there, consequently it did not appear in the plate of patterns in the _Phil.
Trans._ which referred to thumbs. On the other hand, the "banded duplex spiral" (~30~) is common in the thumb, but rare elsewhere. There are some compound patterns, especially the "spiral in loop" (~21~) and the "circlet in loop" (~22~), which are as much loops as whorls; but are reckoned as whorls. The "twinned loop" (~16~) is of more frequent occurrence than would be supposed from the examination of _dabbed_ impressions, as the only part of the outer loop then in view resembles outside arches; it is due to a double separation of the ridges (Plate 4, Fig. 8), and a consequent double inters.p.a.ce. The "crested loop" (~13~) may sometimes be regarded as an incipient form of a "duplex spiral" (~29~).
The reader may also refer to Plate 16, which contains what is there called the C set of standard patterns. They were arranged and used for a special purpose, as described in Chapter XI. They refer to impressions of the right hand.
As a variety of Cores, differing in shape and size, may be found within each of the outlines, it is advisable to describe them separately. Plate 8, Fig. 14 shows a series of the cores of loops, in which the innermost lineations may be either straight or curved back; in the one case they are here called rods (~31~ to ~35~); in the other (~36~ to ~42~), staples. The first of the ridges that envelops the core, whether the core be a rod, many rods, or a staple, is also shown and named (~43~ to ~48~). None of the descriptions are intended to apply to more than the _very end_ of the core, say, from the tip downwards to a distance equal to two average ridge-intervals in length. If more of the core be taken into account, the many varieties in their lower parts begin to make description confusing.
In respect to the "parted" staples and envelopes, and those that are single-eyed, the description may further mention the side on which the parting or the eye occurs, whether it be the Inner or the Outer.
At the bottom of Fig. 14, ~49-54~, is given a series of rings, spirals, and plaits, in which nearly all the clearly distinguishable varieties are included, no regard being paid to the direction of the twist or to the number of turns. ~49~ is a set of concentric circles, ~50~ of ellipses: they are rarely so in a strict sense throughout the pattern, usually breaking away into a more or less spiriform arrangement as in ~51~. A curious optical effect is connected with the circular forms, which becomes almost annoying when many specimens are examined in succession. They seem to be cones standing bodily out from the paper. This singular appearance becomes still more marked when they are viewed with only one eye; no stereoscopic guidance then correcting the illusion of their being contour lines.
Another curious effect is seen in ~53~, which has the appearance of a plait or overlap; two systems of ridges that roll together, end bluntly, the end of the one system running right into a hollow curve of the other, and there stopping short; it seems, at the first glance, to run beneath it, as if it were a plait. This mode of ending forms a singular contrast to that shown in ~51~ and ~52~, where the ridges twist themselves into a point. ~54~ is a deep spiral, sometimes having a large core filled with upright and nearly parallel lines; occasionally they are bulbous, and resemble the commoner "monkey" type, see ~35~.
When the direction of twist is described, the language must be unambiguous: the following are the rules I adopt. The course of the ridge is always followed _towards_ the _centre_ of the pattern, and not away from it. Again, the direction of its course when so followed is specified at the place where it attains its _highest_ point, or that nearest to the finger-tip; its course at that point must needs be horizontal, and therefore directed either towards the inner or the outer side.
The amount of twist has a strong tendency to coincide with either one, two, three, four, or more half-turns, and not to stop short in intermediate positions. Here are indications of some unknown fundamental law, a.n.a.logous apparently to that which causes Loops to be by far the commonest pattern.
The cla.s.sification into Arches, Loops, and Whorls is based on the degree of curvature of the ridges, and enables almost any pattern to be sorted under one or other of those three heads. There are a few ambiguous patterns, and others which are nondescript, but the former are uncommon and the latter rare; as these exceptions give little real inconvenience, the cla.s.sification works easily and well.
Arches are formed when the ridges run from one side to the other of the bulb of the digit without making any backward turn or twist. Loops, when there is a single backward turn, but no twist. Whorls, when there is a turn through at least one complete circle; they are also considered to include all duplex spirals.
[Ill.u.s.tration: PLATE 9.
FIG. 15. TRANSITIONAL PATTERNS--ARCHES AND LOOPS (enlarged three times).]
[Ill.u.s.tration: PLATE 10.
FIG. 16. TRANSITIONAL PATTERNS--LOOPS AND WHORLS (enlarged three times).]
The chief theoretical objection to this threefold system of cla.s.sification lies in the existence of certain compound patterns, by far the most common of which are Whorls enclosed within Loops (Plates 7, 8, Fig. 12, ~15~, ~18~, ~19~, and Fig. 13, ~20-23~). They are as much Loops as Whorls, and properly ought to be relegated to a fourth cla.s.s. I have not done so, but called them Whorls, for a practical reason which is cogent. In an imperfect impression, such as is made by merely dabbing the inked finger upon paper, the enveloping loop is often too incompletely printed to enable its existence to be surely ascertained, especially when the enclosed whorl is so large (Fig. 13, ~23~) that there are only one or two enveloping ridges to represent the loop. On the other hand, the whorled character of the core can hardly fail to be recognised. The practical difficulties lie almost wholly in rightly cla.s.sifying a few transitional forms, diagrammatically and roughly expressed in Fig. 11, ~4~, ~5~, and Fig. 12, ~8~, ~18~, ~19~, with the words "see" so and so written below, and of which actual examples are given on an enlarged scale in Plates 9 and 10, Figs. 15 and 16. Here Fig. 15, _a_ is an undoubted arch, and _c_ an undoubted nascent loop; but _b_ is transitional between them, though nearer to a loop than an arch, _d_ may be thought transitional in the same way, but it has an incipient curl which becomes marked in _e_, while it has grown into a decided whorl in _f_; _d_ should also be compared with _j_, which is in some sense a stage towards _k_. _g_ is a nascent tented-arch, fully developed in _i_, where the pattern as a whole has a slight slope, but is otherwise fairly symmetrical. In _h_ there is some want of symmetry, and a tendency to the formation of a loop on the right side (refer back to Plate 7, Fig. 11, ~4~, and Fig. 12, ~12~); it is a transitional case between a tented arch and a loop, with most resemblance to the latter. Plate 10, Fig. 16 ill.u.s.trates eyed patterns; here _l_ and _m_ are parts of decided loops; _p_, _q_, and _r_ are decided whorls, but _n_ is transitional, inclining towards a loop, and _o_ is transitional, inclining towards a whorl. _s_ is a nascent form of an invaded loop, and is nearly related to _l_; _t_ and _u_ are decidedly invaded loops.
The Arch-Loop-Whorl, or, more briefly, the A. L. W. system of cla.s.sification, while in some degree artificial, is very serviceable for preliminary statistics, such as are needed to obtain a broad view of the distribution of the various patterns. A minute subdivision under numerous heads would necessitate a proportional and somewhat overwhelming amount of statistical labour. Fifty-four different standard varieties are by no means an extravagant number, but to treat fifty-four as thoroughly as three would require eighteen times as much material and labour. Effort is economised by obtaining broad results from a discussion of the A. L. W.
cla.s.ses, afterwards verifying or extending them by special inquiries into a few of the further subdivisions.
[Ill.u.s.tration: PLATE 11.
FIG. 17. ORIGIN OF SUPPLY OF RIDGES TO PATTERNS OF PRINTS OF RIGHT HAND.
FIG. 18. Ambiguities in prints of the Minutiae.]
The divergent ridges that bound any simple pattern admit of nine, and only nine, distinct variations in the first part of their course. The bounding ridge that has attained the summit of any such pattern must have arrived either from the Inner plot (I), the Outer plot (O), or from both.
Similarly as regards the bounding ridge that lies at the lowest point of the pattern. Any one of the three former events may occur in connection with any of the three latter events, so they afford in all 3 3, or nine possible combinations. It is convenient to distinguish them by easily intelligible symbols. Thus, let _i_ signify a bounding line which starts from the point I, whether it proceeds to the summit or to the base of the pattern; let _o_ be a line that similarly proceeds from O, and let _u_ be a line that unites the two plots I and O, either by summit or by base.
Again, let two symbols be used, of which the first shall always refer to the summit, and the second to the base of the pattern. Then the nine possible cases are--_uu_, _ui_, _uo_; _iu_, _ii_, _io_; _ou_, _oi_, _oo_.
The case of the arches is peculiar, but they may be fairly cla.s.sed under the symbol _uu_.
This easy method of cla.s.sification has much power. For example, the four possible kinds of simple spirals (see the 1st, 2nd, and the 5th and 6th diagrams in the lowest row of Plate 11, Fig. 17) are wholly determined by the letters _oj_, _jo_, _ij_, _ji_ respectively. The two forms of duplex spirals are similarly determined by _oi_ and _io_ (see 4th and 5th diagrams in the upper row of Fig. 17), the two slopes of loops by _oo_ and _ii_ (3rd and 4th in the lower row). It also shows very distinctly the sources whence the streams of ridges proceed that feed the pattern, which itself affords another basis for cla.s.sification. The resource against uncertainty in respect to ambiguous or difficult patterns is to compile a dictionary of them, with the heads under which it is advisable that they should severally be cla.s.sed. It would load these pages too heavily to give such a dictionary here. Moreover, it ought to be revised by many experienced eyes, and the time is hardly ripe for this; when it is, it would be no difficult task, out of the large number of prints of separate fingers which for instance I possess (some 15,000), to make an adequate selection, to enlarge them photographically, and finally to print the results in pairs, the one untouched, the other outlined and cla.s.sified.
It may be asked why ridges are followed and not furrows, the furrow being the real boundary between two systems. The reply is, that the ridges are the easiest to trace; and, as the error through following the ridges cannot exceed one-half of a ridge-interval, I have been content to disregard it. I began by tracing furrows, but preferred the ridges after trial.
_Measurements._--It has been already shown that when both plots are present (Plate 4, Fig. 8, ~4~), they form the termini of a base line, from which any part of the pattern may be triangulated, as surveyors would say.
Also, that when only one plot exists (~3~), and the pattern has an axis (which it necessarily has in all ordinary _ii_ and _oo_ cases), a perpendicular can be let fall upon that axis, whose intersection with it will serve as a second point of reference. But our methods must not be too refined. The centres of the plots are not determinable with real exactness, and repeated prints from so soft a substance as flesh are often somewhat dissimilar, the one being more or less broadened out than the other, owing to unequal pressure. It is therefore well to use such other more convenient points of reference as the particular pattern may present. In loops, the intersection of the axis with the summit of the innermost bend, whether it be a staple or the envelope to a rod (Fig. 14, second and third rows of diagrams), is a well-defined position. In spirals, the centre of the pattern is fairly well defined; also a perpendicular erected from the middle of the base to the outline above and below (Fig. 8, ~4~) is precise and convenient.
In prints of adults, measurements may be made in absolute units of length, as in fractions of an inch, or else in millimetres. An average ridge-interval makes, however, a better unit, being independent of growth; it is strictly necessary to adopt it in prints made by children, if present measurements are hereafter to be compared with future ones. The simplest plan of determining and employing this unit is to count the number of ridges to the nearest half-ridge, within the s.p.a.ce of one-tenth of an inch, measured along the axis of the finger at and about the point where it cuts the _summit_ of the outline; then, having already prepared scales suitable for the various likely numbers, to make the measurements with the appropriate scale. Thus, if five ridges were crossed by the axis at that part, in the s.p.a.ce of one-tenth of an inch, each unit of the scale to be used would be one-fiftieth of an inch; if there were four ridges, each unit of the scale would be one-fortieth of an inch; if six ridges one-sixtieth, and so forth. There is no theoretical or practical difficulty, only rough indications being required.
It is unnecessary to describe in detail how the bearings of any point may be expressed after the fashion of compa.s.s bearings, the direction I-O taking the place of East-West, the uppermost direction that of North, and the lowermost of South. Little more is practically wanted than to be able to describe roughly the position of some remarkable feature in the print, as of an island or an enclosure. A ridge that is characterised by these or any other marked peculiarity is easily identified by the above means, and it thereupon serves as an exact basis for the description of other features.
_Purkenje"s "Commentatio."_
Reference has already been made to Purkenje, who has the honour of being the person who first described the inner scrolls (as distinguished from the outlines of the patterns) formed by the ridges. He did so in a University Thesis delivered at Breslau in 1823, ent.i.tled _Commentatio de examine physiologico organi visus et systematis cutanei_ (a physiological examination of the visual organ and of the cutaneous system). The thesis is an ill-printed small 8vo pamphlet of fifty-eight pages, written in a form of Latin that is difficult to translate accurately into free English.
It is, however, of great historical interest and reputation, having been referred to by nearly all subsequent writers, some of whom there is reason to suspect never saw it, but contented themselves with quoting a very small portion at second-hand. No copy of the pamphlet existed in any public medical library in England, nor in any private one so far as I could learn; neither could I get a sight of it at some important continental libraries. One copy was known of it in America. The very zealous Librarian of the Royal College of Surgeons was so good as to take much pains at my instance, to procure one: his zeal was happily and unexpectedly rewarded by success, and the copy is now securely lodged in the library of the College.
_The t.i.tle_
Commentatio de Examine physiologico organi visus et systematis cutanei quam pro loco in gratioso medicorum ordine rite obtinendo die Dec. 22, 1823. H.X.L.C. publice defendit Johannes Evangelista Purkenje, Med.
doctor, Phys. et Path. Professor publicus ordinarius des. a.s.sumto socio Guilielmo Kraus Medicinae studioso.
_Translation_, p. 42.
"Our attention is next engaged by the wonderful arrangement and curving of the minute furrows connected with the organ of touch[4] on the inner surfaces of the hand and foot, especially on the last phalanx of each finger. Some general account of them is always to be found in every manual of physiology and anatomy, but in an organ of such importance as the human hand, used as it is for very varied movements, and especially serviceable to the sense of touch, no research, however minute, can fail in yielding some gratifying addition to our knowledge of that organ. After numberless observations, I have thus far met with nine princ.i.p.al varieties of curvature according to which the tactile furrows are disposed upon the inner surface of the last phalanx of the fingers. I will describe them concisely, and refer to the diagrams for further explanation (see Plate 12, Fig. 19).
1. _Transverse flexures._--The minute furrows starting from the bend of the joint, run from one side of the phalanx to the other; at first transversely in nearly straight lines, then by degrees they become more and more curved towards the middle, until at last they are bent into arches that are almost concentric with the circ.u.mference of the finger.
2. _Central Longitudinal Stria._--This configuration is nearly the same as in 1, the only difference being that a perpendicular stria is enclosed within the transverse furrows, as if it were a nucleus.