312 THE SENSES, 



Touch is not only the most simple, but the most reliable 

 of the senses. Vision, hearing, smell, taste, may easily be de- 

 ceived, but rarely touch. Still, even this sense is not wholly 

 absolved from fallacies. No ideas are more distinct to the 

 mind than those of heat and cold ; yet the sensations of 

 extreme heat and extreme cold are so nearly allied, that they 

 seem identical. 



Frozen mercury imparts the sensation of burning to the 

 surface it touches; and, less markedly, so does contact with 

 a metal surface when the weather is very cold. The chief 

 indications of this sense are the qualities of hardness, softness, 

 heat, cold, levity, weight, smoothness, and roughness, in their 

 various degrees, from pleasure up to pain. 



Through touch we experience most of the ordinary cor- 

 poreal pains to which we are subject ; nevertheless, each of 

 the remaining senses can beget these opposite impressions. 

 Strange though it may seem, the limits between corporeal 

 pleasure and pain are by no means clear. To illustrate by 

 the sense of touch, tickling is an example. In respect to 

 taste, experience of mustard, pepper indeed any condiment 

 testifies. 



Moderate light is pleasing, brilliant light pains ; the sweet- 

 est of odours become unpleasant when too powerful; and 

 though music in a general way be agreeable, it may become a 

 nuisance : for testimony of which I appeal to Mr. Babbage. 



A curious circumstance affecting touch is, that the greater 

 portion of the brain, largest of all the nervous centres, is 

 completely insensible. Instances are on record of the upper 

 parts of the human brain having been sliced away, not only 

 without infliction of pain, but without any seeming injury to 

 the patient. 



Haller proved that tendons, cartilages, and bones, whilst 

 healthy, are quite insensible. Either, when diseased, may be- 

 come the seat of acute pain. Muscle in ordinary language, 

 ftesli is far less sensitive than skin. The surgical operation 



