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SCIENCE. 



[N. S. Vol. XIX. No. 477. 



gether, however, form a unitary paper, and it 

 will be more convenient to analyze them to- 

 gether. The primary object of the research 

 is an investigation into the possibility of any 

 true measurement of tactile sensitivity. 



(a) Introductory Discussion; Methods. — 

 The different meanings of the term sensitivity 

 are discussed. Much space is given to an 

 account of Weber's researches, a little to that 

 of his successors. Tav^ney's recent analysis 

 of the Vexirfehler (mistaking of one point 

 for two) is vei-y significant, and really throws 

 doubt on the very possibility of determining a 

 threshold. There have been grave errors of 

 method in all previous researches. The ses- 

 thesiometer should be one capable of exerci- 

 sing a known and equal pressure on both points 

 stimulated; of stimulating them simultane- 

 ously, or, in case simultaneity is not attained, 

 of registering the fact; and of regulating and 

 recording the rapidity of application of the 

 stimuli. The author describes such an instru- 

 ment. The method of minimal changes is 

 faulty in that it introduces suggestion strongly 

 and gives the subject too slow an adaptation to 

 the difference between the feelings attending 

 small and large distances between the points. 

 The threshold given by the method of right 

 and wrong cases is a mere convention. A 

 mixed method, that of irregular variations, is 

 preferable. It consists in arranging a series 

 of minimal differences, but applying them in 

 irregular yet uniformly determined order. 

 There is a serious disadvantage in employing 

 as subjects laboratory students exclusively. 

 Most important of all is the giving of full psy- 

 chological indications. It is necessary to take 

 account of the subject's degree of acquaintance 

 with sesthesiometry, and of everything that is 

 said and done which has any relation to the 

 study of tactile sensitivity. It is a mistake to 

 confine the responses of the subject to the 

 simple words one and tivo, and when he is 

 doubtful, to make him guess or to count the 

 doubtful cases half to the correct and half 

 to the incorrect replies. A long and minute 

 analysis of everything that is felt should be 

 exacted, since the states of consciousness are 

 very complex and variable. It is essential to 

 guard against distraction and to recognize it 



when it occurs; this can, perhaps,, be accom- 

 plished best by requiring the subject to esti- 

 mate the distances between the points. This 

 procedure has the further advantage of fur- 

 nishing a control as to the correctness of the 

 replies concerning the number of the contacts. 

 The author quotes frequently from his records 

 of every word that was spoken during his sit- 

 tings and of all facts that might have any pos- 

 sible bearing upon them, and the insights 

 gained thereby into the intricacies of the con- 

 scious processes and into the influence of sug- 

 gestions of all sorts, revealing facts to which a 

 bare enumeration of numerical results would 

 have given no clue, amply justify his insist- 

 ence on the essential importance of such 

 records. 



(b) The Simplists. — There are certain per- 

 sons who make no errors for the single point 

 (no Vexirfehler) ; few errors for points sep- 

 arated by small distances (i. e., they call them 

 almost uniformly one) ; whose threshold is 

 obtuse and well-defined; and who after prac- 

 tise lose their exact perception of the single 

 point and begin to make mistakes. These the 

 author calls ' les simplistes.' Now Claviere 

 has shown that between the definite sensation 

 of a single point (A) and that of two distinct 

 points (C) there exists a series of intermediate 

 sensations (B) of a single contact of varying 

 thickness. The simplists are those who inter- 

 pret sensations B as meaning a single contact, 

 whether or not they know that all the stimula- 

 ting points are of the same thickness. The 

 author found such among school children, who 

 were informed in advance that only one or 

 two stimulating points were to be used and 

 that the number of stimulating points felt was 

 the information desired of the subject; and 

 among adults to whom absolutely no prelim- 

 inary instructions were given, who knew noth- 

 ing of Eesthesiometry, nothing of the nature 

 of the points used nor of the object of the ex- 

 periment, and who, after a long series in which 

 they had at first occupied themselves with 

 considering the character of the stimulating 

 object or with the thought of possible painful 

 sensations that might be inflicted, arrived 

 spontaneously at the idea of indicating the 

 number of contacts that were felt. The ab- 



