432 INNERVATION. [CHAP*, xiv. 



spends very nearly with their relative capacities of touch. Weber 

 discovered that the lips are better estimators of weight than any 

 other part, as we might have anticipated from their delicate sense 

 of touch and their extreme mobility. The fingers and toes are also 

 very delicate instruments of this description. The palms and soles 

 possess this power in a very considerable degree, especially over the 

 heads of the metacarpal and metatarsal bones ; while the back, 

 occiput, thorax, abdomen, shoulders, arms, and legs, have very little 

 capacity of estimating weight. 



Heat and cold are pecular sensations excited by alterations of 

 temperature on the surface of the body. They are, beyond all 

 other sensations, of a relative rather than of an absolute kind, and 

 are always most marked in contrast. Thus, in the familiar experi- 

 ment of dipping one hand into hot, and the other into cold water, 

 and then plunging them both into water of an intermediate tem- 

 perature, the new medium will seem cold to the former and hot to 

 the latter ; and natives of the polar and tropical regions of the globe 

 will respectively complain of the warmth or chilliness of our tem- 

 perate climate when they visit our shores. But it is observable 

 that the sensations of heat and cold, when exalted in degree, 

 resemble each other very nearly. The susceptibility to both is 

 greatest within moderate limits ; and impressions of either, when 

 acute and powerful, amount to pain, and soon cease to be distin- 

 guishable from one another. 



Temperature appears higher in degree when it is applied to a 

 larger surface : thus water feels hotter when we put our whole 

 hand into it, than when we only dip a finger ; the extent of the 

 sensation augmenting the intensity with which it is appreciated, 

 perhaps by more forcibly attracting the attention. 



Sensations of temperature have been usually, and we believe pro- 

 perly, attributed to the nerves of common sensation. These sensa- 

 tions are certainly quite different from touch, both in their peculiar 

 characters and in the source of excitement ; but no less may be 

 said of various other modifications of common sensation, to which it 

 is impossible to assign nerves of special endowment. The existence 

 of fibres fitted to be acted on by heat and cold, but by no other sti- 

 mulus, may be fairly doubted so long as they are undistinguishable 

 from those of touch both at their origin from the nervous centre 

 and in their peripheral distribution. Still, however, it may be noted, 

 that in certain states of paralysis, the sensibility to heat and cold 

 may be destroyed, while common sensation and touch remains."* 

 * See an instructive case by Dr. W. Budd, in the Med. Chir. Trans, vol. xxii. 





