282 THE SPECIAL SENSES. 



ing the sense of pain. He quotes other cases in which the reverse 

 dissociation occurred, pressure sense alone remaining. The simplest 

 explanation of these facts is the view that each pressure, pain, 

 warm, and cold spot is supplied by its own nerve fiber, and that 

 each, when stimulated, reacts, if it reacts at all, only with its own 

 peculiar quality of sensation. According to this view, artificial 

 stimulation, if properly controlled, of the trunks of the nerves 

 supplying the skin should be capable of bringing out these different 

 sense qualities. Experiments made with this point in view have 

 not, however, been very successful. Mechanical or electrical stimu- 

 lation of the ulnar nerve, for instance, gives usually only pain sensa- 

 tions, although if the stimulus is feeble contact sensations are 

 aroused. The method, however, is probably at fault. In the case 

 of amputated fingers or limbs a more decisive result is obtained. 

 As is well known, individuals after such operations may for many 

 years have sensations of their lost fingers or limbs. In such cases 

 the pressure in the stump of the wound acting upon the central ends 

 of the sensory fibers arouses sensations which are projected in the 

 usual way, and give the feeling that would be experienced if the 

 lost parts were still there and were stimulated in the normal manner. 

 The Temperature Senses. The main facts regarding the 

 distribution of heat and cold spots have been determined, but 

 in most of the experiments on record no distinction was made 

 between protopathic temperature sensations and those mediated 

 by the epicritic temperature nerves. It is difficult to adapt 

 the older descriptions to this newer terminology, but when not 

 otherwise specifically stated it may be assumed that the epicritic 

 system is referred to. In general, the cold spots are more 

 numerous than the warm spots, and react more promptly to 

 their adequate stimulus. The threshold stimulus varies in 

 different parts of the skin, the tip of the tongue requiring the 

 smallest stimulus to arouse a sensation, and the eyelids, fore- 

 head, cheeks, lips, limbs, and trunk following in the order 

 named. According to Goldscheider, the spots on most portions 

 of the skin form chains that have a somewhat radiate arrange- 

 ment with reference to the hair follicles. The temperature 

 points possess each its adequate stimulus, that for the 

 cold spot being temperatures lower than the skin or of the terminal 

 organ of the cold nerves, that for the heat spots temperatures higher 

 than their own. From the standpoint of specific nerve ener- 

 gies it is most interesting to find that these points, particularly 

 the cold spots, may be stimulated by other than their adequate 

 stimuli. Mechanical and electrical stimulation has, in the hands of 

 several observers, been efficient in causing a sensation of cold upon 

 a cold spot and of heat upon a warm spot. Some chemical stimuli 

 are also effective. Menthol applied to the skin gives a cold sensa- 



