636 THE SENSES 



temperature. Thus, by plunging the elbow into a bath, a practised bath- 

 attendant can tell the temperature sometimes within half a degree centigrade. 



The temperatures which can be readily discriminated are between 10 and 

 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 

 pleasurable 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-stimulation 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 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 



