April 10, 1908] 



SCIENCE 



583 



be a most valuable addition to our knowledge. 

 Unfortunately, we are left in doubt as to tbese 

 points. 



Further, in view of the fact that the whole 

 treatise is upon the subject of the sense of 

 touch, there is a singular lack of all study or 

 delineation of the nerve supply to the skin 

 and the nature and distribution of nerve end- 

 ings. This study the author says is not neces- 

 sary to the present treatment of the subject; 

 and yet later he bases his argument that the 

 ridges are tactile organs upon the arrange- 

 ment of the papillae of the corium, which he 

 at the same time admits are, many of them, 

 merely vascular networks. It would seem that 

 the elaborate and careful work already done by 

 Dogiel and others upon the nerve structures 

 of the skin of mammals might at least have 

 been allowed to shed some light upon this 

 subject. 



Dr. Kidd finds an interesting imbricated 

 form of ridge structure occurring somewhat 

 sporadically not only in man, but in occasional 

 cases of the lower primates. Also in the ease 

 of the lower mammals a few individuals were 

 found in which occurred similar imbrication 

 of the papillae of the corium. This imbrica- 

 tion is in no case a specific character; it is in 

 some cases proximal, in others distal even 

 upon the same region, though there seems to 

 be a certain degree of constancy in direction 

 in man, at least, the imbrication on the finger 

 tips, when it occurs, being more often distal, 

 and on the hallucal region of the foot, prox- 

 imal. 



In part III. the author strongly adheres to 

 the view of Schlaginhaufen that the ridged 

 form of epidermis has essentially and pri- 

 marily a tactile function instead of the 

 mechanical one first suggested by Hepburn, 

 and later elaborated by Miss Whipple. This 

 latter writer, whose views Dr. Kidd strenu- 

 ously attempts to refute, believes that the 

 ridges are formed by the coalescence of epi- 

 dermic units (modified scales) in response to 

 external pressure conditions, and that they 

 I)erform the fimction of presenting a rough- 

 ened surface to increase friction and thus pre- 

 vent slipping either in walking or prehension, 

 hence the term "friction skin." According 



to this interpretation there is no attempt to 

 minimize the importance of the general tactile 

 function of the regions in question, since in 

 the very nature of the case they are especially 

 exposed to contact with external objects. The 

 arrangement of the papillse of the corium in 

 double rows underlying the ridges is, however, 

 regarded as merely incident to the fact that, 

 in the primate type at least, enormously large 

 sweat glands are arranged in a row underlying 

 each ridge and opening upon its surface, thus 

 by their secretion adding greatly to the effi- 

 ciency of the friction skin in prehension. Of 

 necessity, then, the papillae must occupy the 

 only remaining space, which is upon either 

 side of the line of sweat glands and hence 

 follows also the course of the ridges. 



After this brief exposition of the view which 

 Dr. Kidd would refute, let us return to his 

 arguments. He makes no attempt whatever 

 to account for the large number and great size 

 of the sweat glands associated with the ridges ; 

 but from the fact that the papillas, many of 

 which are indeed merely vascular, are ar- 

 ranged in rows underlying the ridges, he 

 argues that the ridges themselves must be 

 tactile organs. Neither does he seem to see 

 that the great thickness of the epidermis over 

 ridged areas (which certainly can not be for 

 the purpose of increasing the sensitiveness of 

 the skin) must in part account for the neces- 

 sity for more numerous and taller papillae 

 than in more thinly covered regions of equal 

 sensitiveness. It is just at this point that we 

 feel the author's mistake in not including in 

 his work a careful study of the nerve struc- 

 tures of the skin. 



Neither is there any satisfactory experi- 

 mental basis presented to show that the ex- 

 ternal epidermic ridged structure actually 

 does add to the tactile function. This is, 

 indeed, a point upon which such trustworthy 

 experimental psychologists as Stern and Fere 

 absolutely disagree. The only possible rela- 

 tionship which any one has attempted to estab- 

 lish between the direction of the ridges and 

 the sensitiveness of the surface is that referred 

 to by Dr. Kidd, which lies in the fact that two 

 points seem to be more readily distinguished 

 when so placed that a line joining them is at 



