THE TEMPERATURE SENSE. 



837 



wooden cups with a metallic base, and filled with warm and cold water, the temperature being 

 registered by a thermometer placed in the cups. [2. Clinically, two test-tubes filled with 

 cold and warm water, or two spoons, the one hot and the other cold, may be used.] 



Results. 1. As a general rule, the feeling of cold is produced when a body 

 applied to the skin robs it of heat ; and, conversely, we have a sensation of warmth 

 when heat is communicated to the skin. 



2. The greater the thermal conductivity of the substance touching the skin, the 

 more intense is the feeling of heat or cold ( 218). 



3. At a temperature of 15*5 -35 C, we distinguish distinctly differences of 

 temperature of , 2-0 , 16 R. with the tips of the fingers (E. H. Weber). Tem- 



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Fig. 622. 

 Cold- and hot-spots from the same part of the anterior surface of the fore-arm. a, cold-spots ; 

 b, hot-spots. The dark parts are the most sensitive, the hatched the medium, the dotted 

 the feebly, and the vacant spaces the non-sensitive. 



peratures just below that of the blood (33-27 C. Nothnagel) are distinguished 

 most distinctly by the most sensitive parts, even to differences of 0*05 C. (Linder- 

 mann). Differences of temperature are less easily made out when dealing with 

 temperatures of 33-39 C, as well as between 14-27 C. A temperature of 

 55 C, and also one a few degrees above zero (2*8 C), cause distinct pain in 

 addition to the sensation of temperature. 



4. The sensibility for cold is generally greater than for warmth, that of the left 

 hand is greater than the right (Goldscheider). The different parts of the skin also 

 vary in the acuteness of their thermal sense, and in the following order : Tip 

 of the tongue, eyelids, cheeks, lips, neck, and body. The perceptible minimum 

 Nothnagel found to be 0*4 on the breast ; 0*9 on the back ; 0*3, back of the 

 hand ; 0*4, palm ; 0*2, arm ; 0'4, back of the foot ; 0*5, thigh j 0*6, leg ; 

 0*4 o -0'2 o , cheek ; 0'i-0'd C, temple. The thermal sense is less acute in the 

 middle line, e.g., the nose, than on each side of it (E. H. Weber). Fig. 622 shows 

 that in one and the same portion of skin, the cold- and hot-spots are differently 

 located, i.e., their different topography. 



If the mucous membrane of the mouth be pencilled with a 10 per cent, solution of cocain,- the 

 sensibility for heat is abolished ; the cooling sensation of menthol depends upon its stimu- 

 lation of the cold nerves ; C0 2 applied to the skin excites the heat nerves (Goldscheider). 



5. Differences of temperature are most easily perceived when the same part of the 

 skin is affected successively by objects of different temperature. If, however, two 



