CUTANEOUS SENSES OF COLD AND WARMTH. 945 



Touches may be perceived as of separate locus, though their mutual 

 direction be imperceptible ; a line 9 mm. long is perceived by touch as 

 linear, but for the direction to be perceived must exceed 12 mm. 

 Alphabets for the blind have linear or punctate letters. The threshold 

 of space for recognition of line direction is more than twice as high as 

 for successive points. The dimensional distances being the same, the 

 point alphabet is therefore the easier, especially if the points be taken in 

 succession as in the New York horizontal point-letters; the Braille 

 point-letters are vertical. 



The central paths and centres concerned with the conduction and 

 elaboration of the nervous reactions of " touch " are dealt with in the 

 sections dealing with the " spinal cord " and the " cerebral cortex." 



Reaction-Time.— The reaction-time for touch is longer on the average 

 than that for audition, shorter than that for vision. The average time 

 observed by Exner was •1337 seconds, by Hankel 1546 seconds, by 

 Baldwin 125 seconds, by Hirsch 182 seconds, by Wundt 213 seconds. 

 The reaction-time for electric skin stimuli is shorter than for tactile, 

 thus Wundt '201 seconds ; l for tactile shorter than for cold and warm. 

 But the experiments have too many psychological factors to warrant 

 discussion here. 



Cutaneous Senses of Cold and Warmth. 



Eecent evidence has led to the cutaneous sensations of cold and 

 warmth being regarded as specific and distinct from tactual sensations, 

 and from each other. 



"Cold." and "warmth" as distinct species of sense. — This view 

 implies that even a " localised " cold (or warmth) sensation possesses no 

 tactual element, and that a cold (or warm) stimulus, e.g. the point of a 

 cooled (or heated) metal pencil applied to a " cold spot " (or to a 

 " warmth spot " respectively), acts there not at all as a tactile stimulus. 

 Much has been brought forward in support of such a view. It is in 

 some ways more in accord with what we should expect from intro- 

 spective examination, to regard the sensations we derive from the skin 

 as all of them sensations of greater or less tactual intensity, some of 

 them, however, inseparably accompanied, as it were coloured, by qualities 

 of sensation which we call " cold " and " warmth," others not so accom- 

 panied or coloured. There is much to show that while we possess 

 sensations of brightness quite uncoloured, the sensations of colour we 

 possess are all of them inseparable from sensation of brightness. 

 If each sensation of " cold " or " warmth " is a concomitant inseparable 

 from a tactual sensation, it is simpler to treat it not as a separate 

 species of sensation, but as a quality of tactual sensation. The 

 weight of evidence seems at present, however, to be against this. 

 It can be urged against it that thermal stimuli unaccompanied by 

 any tactile element (e.g. radiant heat), or accompanied by only such as 

 lie far below the threshold value of tactile stimuli, can yet excite 

 strong " cold " and " warmth " sensations. On the other hand, to some 2 

 even warm vapour moving over the skin gives a sensation that they 

 describe as having some tactual character as well as the character 

 of " warmth." 



1 "Physiolog. Psychol.," Leipzig, 1893, Bd. ii. S. 223. 



2 See Eugenio Tanzi, "Sulle sensazioni del freddo e del caldo," Milano-Torino, 1886. 



VOL. II. — 60 





