584 



SCIENCE 



[N. S. Vol. XXVII. No. 693 



right angles to the general course of the ridges. 

 The author apparently does not see, however, 

 that such a result is quite in accord with the 

 very ideas which he is trying to refute. Miss 

 Whipple has shown that the friction ridges 

 are so arranged as to be at right angles to the 

 usual direction of pressure, and naturally the 

 correlated tactile function would tend to be 

 most highly developed along these same lines 

 of pressure. This, indeed, is very probably 

 purely the result of practise; for the ejrperi- 

 ments of Volkmann. and Dresslar have shown 

 that a given region of the skin has power to 

 increase in sensitiveness by practise to an 

 extent far exceeding the slight differences in 

 sensitiveness which seem to be associated with 

 the direction of the ridges. The fact that 

 many ridged areas, such as, for example, the 

 ball of the foot, where the ridges are markedly 

 high and distinct and the patterns which they 

 form are very complex and varied, are found 

 to be low in the scale of relative sensitiveness 

 should in itseK show that the ridges serve pri- 

 marily a mechanical and not a tactile func- 

 tion. 



Dr. Kidd brings forward a list of instances 

 in which ridges are formed upon unaccus- 

 tomed places, where, he says, they can have 

 no prehensile function. However, as he him- 

 self is forced to intimate, these instances of 

 ridge formation can certainly be attributed 

 to the influence of external pressure, and 

 there is no doubt that many of them are valu- 

 able observations showing that ridges do form 

 in response to such pressure. Certainly some 

 of the regions mentioned do not possess 

 a degree of sensitiveness which would 

 justify the creation of highly specialized 

 sense organs. 



Others of Dr. Kidd's arguments are so 

 plainly fallacious that they need only be men- 

 tioned. For instance, he says, " arches, loops, 

 and whorls represent degrees of departure 

 from the primitive arrangement, and enable 

 a larger area of ridge-covered surface to be 

 exposed to contact relatively to the size of the 

 part." One can hardly see how the form of 

 pattern can increase the area of the surface, 

 provided that in each case the surface is cov- 

 ered with ridges. 



Again he argues : " The pulps of man's 

 fingers have highly developed patterns, and 

 these are more variable and complex than 

 those of any other part of any of the primates, 

 and these are the most sensitive areas in any 

 hand or foot. In this instance the connection 

 between sensibility and complexity of pattern 

 of ridges is intimate. The pulps of the toes 

 in man are less sensitive than those of the 

 fingers, and the patterns of the second, third, 

 fovirth and fifth digits simple, and these digits 

 are relatively weak in function compared with 

 the hallux." One has only to turn over the 

 pages of Dr. Kidd's own book to see many 

 illustrations of patterns on the interdigital 

 and proximal pads of monkeys which repre- 

 sent not only perfect whorls, but many other 

 very intricate and complicated patterns. Fur- 

 thermore, in the study of many hundreds of 

 human hands and feet, the most complicated 

 patterns which the reviewer has found have 

 been upon the apical pads of all five of the 

 toes; these patterns are, however, very large 

 and one must study the lateral sides of the 

 digit as well as the mere contact surface, in 

 order to appreciate them. 



The author presents, also, as an argument 

 in favor of the tactile function of the ridges,, 

 the fact of their imbrication above referred 

 to. This, he avers, must have some important 

 significance in relation to the sense of touch, 

 though he is unable to show how. It is a little 

 surprising that so strong a Lamarckian as he 

 has shown himself to be by his previous 

 writings should fail to see, in this imbrication, 

 a Lamarckian character due to external pres- 

 sure, a pressure which would be the resultant 

 of the shape of the surface and the amoimt 

 and kind of use of the region involved. Two 

 eases cited in which the imbrication has a 

 definite relationship to the center of the core 

 of the pattern, being toward the center in one 

 case and away from it in the other, would thus 

 find a possibility of explanation; while on the 

 basis of some important tactile function the 

 two cases absolutely defeat each other. 



As a whole the book is a timely contribu- 

 tion to a subject which has recently come into 

 renewed prominence, and with its excellent 

 illustrations and extensive bibliography, is. 



