THE TEMPERATURE-SENSE. 



there will be the sensation of warmth; under opposite conditions, the 

 sensation of cold. The greater the deviation of the thermal apparatus 

 from its zero-temperature, the more distinct or the more intense will 

 be the sensation of heat or cold. The zero-point may, however, be 

 displaced quite rapidly within certain limits as a result of external 

 conditions. 



Method of Examination. Areas of the skin are successively touched with 

 objects of different temperature, of equal size and possessing equal heat-con- 

 ducting powers, (i) Nothnagel employs for this purpose small wooden cups, 

 with metal bottoms, which are filled with cold or warm water, and are placed on 

 the skin; the temperature of the water is indicated by a thermometer. (2) Two 

 thermometers, which are heated unequally (if necessary by electrical means), 

 can be applied directly to the skin for comparison. 



The following facts have been ascertained with regard to the tem- 

 perature-sense : 



i. In general, the feeling of cold arises when a body applied to the 

 skin withdraws heat, and, conversely, that of warmth, when heat is 

 communicated to the skin. 



2 The greater the heat-conducting power of the body touching 

 the skin the more intense is the feeling of heat or of cold. 



3. Between the limits of 15.5 and 35 C. the finger-tips are able 

 to distinguish differences of temperature of from 0.20 to 0.25 C. The 

 temperatures most exactly determined are those that lie close to the 

 temperature of the blood (from 33 to 27 C.), differences as small as 0.05 

 C. being recognized (in the most sensitive situations). Temperatures 

 between 33 and 39 C. and also those between 14 and 27 C. are less 

 accurately determined. Temperatures of 52.6 C. and 4-2.8 C. and 

 lower cause in addition to the temperature-sensation, marked pain, 

 but in this respect there are variations in different individuals, and in 

 different places between 11.4 and +36.3 C. 



4. The sensitiveness for cold is in general greater than that for 

 heat, and greater on the left hand than on the right. The different 

 portions of the skin differ in their acuteness of heat-perception, and 

 in the following order: tip of the tongue, eyelids, cheeks, lips, neck, 

 trunk. Nothnagel found the minimum of differentiation on the chest 

 0.4, on the back 0.9, on the back of the hand 0.3, on the palm 0.4, 

 on the arm 0.2, on the back of foot 0.4, on the thigh 0.5, on the leg 

 0.6, on the cheek from 0.4 to 0.2, on the temple from 0.4 to 0.3 C. 

 Curiously, the skin in the median line (for example of the nose) has a 

 less acute heat-perception than the lateral portions (alae of the nose). 

 According to Dessoir, the glans penis has no perception of heat. 



Fig- 343 shows the difference in the topographical arrangement of 

 the heat-sense and the cold-sense on the same portion of the skin. 



Goldscheider assumes 12 empirically determined grades of sensitiveness for 

 the perception of cold, and 8 for that of heat. Each part of the skin has a 

 comparatively constant grade of sensitiveness. For example, the skin of the 

 mammilla has the grade n for cold-perception, the grade 8 for heat-perception; 

 the middle of the sole of the foot respectively 7 and 2 . 



Application of a 10 per cent, solution of cocain to the tongue and the mucous 

 membrane of the mouth abolishes completely the sensibility for heat and cold. 

 L he cooling sensation due to menthol depends upon stimulation of the nerves for 

 cold; carbon dioxid irritates the heat-nerves of the external skin. 



5. The differences in temperature are best recognized when different 

 degrees of temperature are applied to one portion of the skin in rapid 



