860 OF SENSATION, AND THE ORGANS OF THE SENSES. 



notions which we should derive from the sense of Sight, if used alone. On the 

 other hand, it must be confessed that our knowledge would have a very limited 

 range, if this sense were the only medium through which we could acquire 

 ideas. It is probably on the sensations communicated through the Touch, that 

 the idea of the material world, as something external to ourselves, chiefly rests ; 

 but this idea is by no means a logical deduction from our experience of these 

 sensations, being rather an instinctive or intuitive perception directly excited 

 by them ( 790). 



866. That the conditions under which certain of the modifications of common 

 sensation operate, are in some respects different from those of ordinary Touch, 

 is very easily shown. Thus, the feeling of tickling is excited most readily in 

 parts which have but a low tactile sensibility, namely, the armpits, flanks, and 

 soles of the feet; whilst in the points of the fingers, whose tactile sensibility is 

 most acute, it cannot be excited. Moreover, the nipple is very moderately 

 endowed with ordinary sensibility; yet by a particular kind of irritation, a very 

 strong feeling may be excited through it. Again, in regard to Temperature, it 

 is remarked by Weber that the left hand is more sensitive than the right : 

 although the sense of touch is undoubtedly the more acute in the latter. He 

 states that, if the two hands, previously of the same temperature, be plunged 

 into separate basins of warm water, that in which the left hand is immersed 

 will be felt as the warmer, even though its temperature is somewhat lower than 

 that of the other. In regard to the sensations of heat and cold, he points out 

 another curious fact that a weaker impression made on a large surface, 

 seems more powerful than a stronger impression made on a small surface ; 

 thus, if the forefinger of one hand be immersed in water at 104, and 

 the whole of the other hand be plunged in water at 102, the cooler water 

 will be thought the warmer ; whence the well-known fact that water in which a 

 finger can be held will scald the whole hand. Hence it also follows that minute 

 differences in temperature, which are imperceptible to a single finger, are appre- 

 ciated by plunging the whole hand into the water ; in this manner, a difference 

 of one-third of a degree may readily be detected, when the same hand is placed 

 successively in two vessels. The judgment is more accurate, when the temper- 

 ature is not much above or below the usual heat of the body ; just as sounds are 

 best discriminated when neither very acute nor very grave. Some further 

 experiments have recently been made by Professor Weber, to determine whether 

 the sense of> temperature is received through any other channel than the sensory 

 apparatus contained in the integuments. 1 The first means of which he availed 

 himself for deciding this question, was that afforded by the results of accident 

 or surgical operations, in which a portion of skin had been left deficient. Thus, 

 in three cases in which a large portion of the skin had been destroyed by a burn, 

 and in which healing had not advanced so far as to renew the organ of touch, it 

 was found that no correct discrimination could be made between two spatulas, 

 one of them at a temperature of from 48 to 54, the other of from 113 to 122, 

 which were brought into contact with the denuded surface ; so that one of these 

 patients thrice affirmed that he was being touched with the cold body, when it 

 was the warm, and the reverse. But when the spatula was in one instance 

 made somewhat warmer, and was brought into contact with the unskinned sur- 

 face, the patient felt, not heat, but pain. Another means of gaining information 

 on this point is afforded by the ingestion or injection of a large quantity of warm 

 or cold fluid into the stomach or intestinal canal. Thus Professor Weber states 

 that, after drinking a tumbler of water at 32, he felt the cold water in the mouth, 

 in the palate, and in the pharynx, as far as the limits of the sense of touch ; 

 but that the gradual passage of the cold water into the stomach could not be 



i "Miiller's Archiv.," 1849, heft iv. s. 273-283. 



