926 CUTANEOUS SENSATIONS. 



without shock ; 1 by a combination of a delicate spring and beam balance ; 2 

 by applying fine elastic filaments, glass, wool fibres, hairs, etc. 3 An adjustable 

 projection from a smooth subspherical surface has been introduced by Graham 

 Brown, v. Frey 4 has been, as far as I know, the first to employ measured 

 degrees of traction as stimuli. 



Liminal intensity of stimulus. — When a solid body of known 

 weight, with one side smooth and of known area, is warmed to the skin 

 temperature, and allowed, in virtue of its own weight, to rest smooth 

 side downward on the supported hand, it causes a sensation of touch of 

 a certain intensity, i.e. it " touches " with a certain degree of intensity. 

 The intensity of the physical stimulus is easily written in such instances 

 as values of " pressure." The resulting sensations are often, especially 

 when the intensity is somewhat high, termed " pressure sensations." 

 Such pressure sensations are, however, to be regarded merely as degrees 

 of touch sensation. 



Kammler 5 measured the least weights with contact surface of 9 sq. 

 mm. capable of exciting touch sensation at different skin regions. He found 

 •002 grm. liminal for the forehead, temple, and back of hand and fore- 

 arm ; '003 grm. for flexor aspect of forearm ; "005 grm. for lips, chin, 

 eyelids, and abdomen; "01 grm. for palmar surface of fingers; 1 grm. for 

 ankle and finger-nail. It must be remembered, however, that for one 

 and the same region it is found, in actual practice, that the liminal 

 stimulus varies considerably, even when tested by contact areas 7 mm. 

 in diameter ; thus, in the pulp of the finger, at some areas, the liminal 

 intensity is four times greater than at others. 6 Where thick and unyield- 

 ing, the skin will, cceteris paribus, require greater pressure to deform 

 its surface than where thin and supple. The pressure required to evoke 

 sensation is therefore, if deformation of surface (v.s.) be the immediate 

 stimulus, a mode of expression that has for each surface to be interpreted. 



The expression liminal stimulus includes three important values of 

 stimulus, namely, the least stimulus that never fails to evoke sensation, 

 the least stimulus that in the whole series of observed cases does evoke 

 sensation, and the least stimulus that in half the number of observed 

 cases evokes sensation. These are respectively the upper, lower, and 

 median limina. 



The short hairs of the skin much enhance its tactual sensitivity. On 

 9 sq. mm. of skin from which the hairs had been shaved, the liminal 

 stimulus was found to be 36 mgrms., whereas, on the same surface, before 

 it was shaved, 2 mgrms. was the liminal stimulus. The liminal stimulus 

 for the touch spots about a short hair is three to twelve times greater 

 than for the hair itself, i.e. the hair is three to twelve times more sensitive 

 than the " spots." The liminal stimulus for the hair progressively 

 increases as it is progressively cut shorter and shorter. 7 Each short 

 hair is a lever, of which the long arm outside the skin acts at an 

 advantage upon the touch organs at the root. The short hairs are 

 probably the most sensitive tactual organs of the body. 



1 Landois, loc. cit. 2 v. Frey, see Kiesow, loc. cit. 



3 Hensen, " Vortrag gegen den sechsten Sinn," Kiel, 1893 ; v. Frey, op. cit., July 1894. 



4 Op. cit., 1897. 



s " Exper. d. variarum cutis regionuni min. pondera sent, virtute," Diss., Vratislavire, 

 1858 ; also with Aubert in Untersuch. z. Naturl. d. Mensch. u. d. Thiere, 1859, Bd. v. 

 Scripture finds the limina here obtained "quite too low for most people," "New 

 Psychology," London, 1897, p. 284. 



6 Kiesow, loc. n't. 7 v. Frey, loc. cit. 



