836 



THE TEMPERATURE SENSE. 



sensation is felt only at the limit of the fluid, on the volar surface of the finger, at 

 the limit of the surface of the mercury. 



428. TEMPERATTJBE SENSE. The temperature sense makes us aquainted 

 with the variations of the heat of the skin. 



A tpecific end-ajyparatus arranged in a punctated manner is connected with the 

 temperature sense. ; 



These " temperature-spots " are arranged in a linear manner or in chains, which 

 are usually slightly curved (figs. 620, 621). They generally radiate from certain 

 points of the skin, usually the hair-roots. The chain of the " cold-spots " usually 

 does not coincide with those of the " hot-spots," although the point from which they 

 radiate may be the same. Frequently, these punctated lines are not complete, but 

 they may be indicated by scattered points, between which, not unfrequently, points 

 or spots for other qualities of sensation may be intercalated. Near the hairs there 

 are almost always temperature-spots. In parts of the skin, where the temperature 

 sensibility is slight, the temperature-points are present only near the hairs. 



The sensation of cold occurs at once, while the sensation of heat develops 

 gradually. Mechanical and electrical stimulation also excite the sensation of 



(\P. 



W.B 



C.P. 



i 



+ 



W.P. 



Fig. 621. -A, 



C D 



Fig. 620. Fig. 621. 



cold-spots, B, hot-spots, from the volar surface of the terminal phalanx of the 



index-finger to the margins of the nail. Fig. 622. C, cold-spots, and D, warm-spots of the 

 radial half of the dorsal surface of the wrist. The arrow indicates the direction in which 

 the hair points. 



temperature. A gentle touch of the temperature-spots is not perceived ; these 

 joints seem to be anaesthetic towards pressure and pain. As a general rule, the 

 cold-spots are more abundant over the whole body there are more of them in a 

 given area while the hot-spots may be quite absent. The hot-spots are, as a rule, 

 perceived as double at a greater distance apart than the cold-spots. The minimal 

 distance on the forehead is 0"8 mm. for the cold-spots and 4 to 5 mm. for the 

 warm-spots ; on the breast the corresponding numbers are 2 and 4 to 5 ; back, 1 *5 

 to 2 and 4 to 6 ; back of hand, 2 to 3 and 3 to 4 ; palm, 0*8 to 2 ; thigh and leg, 

 2 to 3 and 3 to 4 mm. 



Method. To test the hot- and cold-spots, use a hot or cold metallic rod ; at the cold-spots, 

 when they are lightly touched, only the sensation of cold will be felt, and a corresponding effect 

 with a hot rod at the hot-spots. Both spots are insensible to objects of the same temperature 

 as the skin. 



According to E. Hering, what determines the sensation of temperature is the 

 temperature of the thermic end-apparatus itself, i.e., its zero-temperature. As often 

 as the temperature of a cutaneous area is above its zero-temperature, we feel it as 

 warm; in the opposite case, cold. The one or the other sensation is more marked, 

 the more the one or other temperature varies from the zero-temperature. The zero- 

 temperature can undergo changes within considerable limits, owing to external 

 conditions. 



Methods. To the surface of the skin objects of the same size and with the same thermal 

 conductivity are applied successively at different temperatures : 1. Nothnagel uses small 



