CHAP. vi. J SOME OTHER SENSATIONS. H:',l 



straight up from the peripheral organ to the "seat of conscious- 

 ness." 



In the second place when we do experience sensations of tem- 

 perature the sensation is caused not by the mere change of 

 temperature but by the altered condition of the skin which results 

 from that change. When an area of the skin having a normal 

 temperature is brought in contact with a cold body, the skin 

 undergoes a change from a normal to a lower temperature, and 

 we experience a sensation of cold. Now, if it were only the change 

 from a normal to a lower temperature which gave rise to the 

 sensation, though the sensation might and probably would last 

 much longer than the change itself, it could not be prolonged by 

 the mere maintenance of the lower temperature when once the 

 change had been established. But experience shews that it is ; 

 we still feel a sensation of cold, at a time when the contact of 

 the cold body is not producing any further lowering of temperature 

 and at most is only maintaining the lower temperature already 

 brought about. Nay, more, the sensation of cold continues after 

 the cooling body has been removed, at the time when the skin 

 is returning to its normal temperature, that is to say is undergoing 

 the very opposite change of temperature, namely, one from cold 

 to heat. And the same considerations apply to sensations of heat. 



890. We may conclude then that when the application of 

 cold or of heat to the skin causes a sensation of cold, the cold or 

 heat produces a condition in the material of the skin, which 

 condition starts nervous impulses in the afferent nerves of cold 

 and heat sensations. Since the application of cold or of heat to 

 the nerve fibres underlying the skin does not produce a sensation 

 of cold or heat, but only a sensation of pain, we may further 

 conclude that the material whose condition starts the sensation is 

 placed in the skin itself, in the epidermis or in the immediately 

 underlying dermis. Since we experience sensations of cold and 

 heat in regions of the skin, not only free from touch corpuscles 

 but also free from any dermic terminal organs as yet known, the 

 " points " of the skin determined experimentally to be points of 

 cold and heat sensations, having been repeatedly found when 

 extirpated to be free from all such dermic organs, we may, though 

 with less certainty, still further infer that the material exists 

 somewhere in the epidermis. We may add that sensations of 

 temperature may be felt in the cornea, from which all dermic 

 terminal organs seem certainly to be absent. And our knowledge 

 that the nerve fibres end as fine fibrilla? between and among the 

 cells of the malpighian layer ( 874) brings us to the final con- 

 clusion that the material of which we are speaking is to be 

 sought for either in the fine nerve fibrill* themselves, or, as seems 

 more likely, in some or other of the cells of the malpighian layer 

 specially connected with those fibrillse. 



Beyond this we cannot go ; and even admitting thus much, it 



