602 THE SENSES 



45 C. (50 and 115 F.); very low and very high temperatures alike produce a 

 burning sensation. A temperature appears higher according to the extent of 

 cutaneous surface exposed to it. Thus, water of a temperature which can be 

 readily borne by the hand is quite intolerable if the whole body be immersed. 



The delicacy of the sense of temperature coincides in the main with that 

 of touch, and appears to depend largely on the thickness of the skin; hence, 

 in the elbow, where the skin is thin, the sense of temperature is delicate, 

 though that of touch is not remarkably so. Weber has further ascertained 

 the following facts: two points so near together on the skin that they 

 produce but a single impression, at once give rise to two sensations, when 

 one is hotter than the other. Moreover, of two bodies of equal weight, that 

 which is the colder feels heavier than the other. 



As every sensation is attended with a perception and leaves behind it an 

 idea in the mind which can be reproduced at will, we are enabled to compare 

 the idea of a past sensation with another sensation really present. Thus we 

 can compare the weight of one body with another which we had previously 

 felt, of which the idea is retained in our mind. Weber was indeed able to 

 distinguish in this manner between temperatures experienced one after 

 the other, better than between temperatures to which the two hands were 

 simultaneously subjected. This power of comparing present with past sensa- 

 tions diminishes, however, in proportion to the time which has elapsed between 

 them. After-sensations left by impressions on nerves of common sensibility 

 or touch are very vivid and durable. As long as the condition into which 

 the stimulus has thrown the organ endures, the sensation also remains, though 

 the exciting cause should have long ceased to act. Both painful and pleasur- 

 able sensations afford many examples of this fact. 



Sense of Pain. As regards painful sensations, three views can be 

 taken: i, That it is a special sensation provided with a special conducting 

 apparatus in each part of the body; 2, that it is produced by an over-stimula- 

 tion of the special nerves concerned with touch or temperature, or of the 

 other nerves of special sense; or 3, that it is an over-stimulation of the nerves 

 of common sensation, which tell us of the condition of our own bodies, both 

 of the surface and also of the internal organs. There seems to be much in 

 favor of all of these views. The weight of evidence is, however, rather against 

 there being any special pain sense with a special end-organ and fibers, though 

 Barker in his own arm experienced the presence of pain sensations while 

 there was absence of sensations of touch and temperature. It is, indeed, 

 certain that, even if any variety of pain be a special sensation, some kind of 

 pain may be produced by stimulation of the bare sensory nerves apart from 

 any special form of nerve termination. It is said that the main difference 

 between the common sensory apparatus which tells us of the condition of all 

 parts of the body of which thirst and hunger are but examples, and the 

 special sense of touch and temperature, is that the latter are provided with 



