THERMAL SENSATIONS 



439 



K/iK 



0,03 



0.0! 



0.01 



J L 



^T . 



32 33 30 35 36 37 3S 



Temperature 6 



—is- 



»C ft 



FIG. 5. Rate, d^/d/, of the intracutaneous temperature change 

 at the subsidence of the warm sensation as a function of the 

 prevalent temperature. (Forearm, skin temperature 3 1 °C, 

 thermode area of 20 cm^.) It will be seen that smaller values of 

 d9/d< are necessary for maintaining a warm sensation, the 

 higher the prevailing temperature. [From Hensel C4J).j 



The rate (d0/d/) of the intracutaneous temperature 

 change at the moment of the subsidence of the warm 

 sensation is shown in figure 5. Thus, the rate of temp- 

 erature change beUeved necessary to maintain a sen- 

 sation diminishes the more extreme the temperature 

 until at certain threshold temperatures it attains the 

 value of o. Outside this threshold value a constant 

 temperature acts as a stimulus eliciting a steady 

 thermal sensation. 



The experiments of Gertz (30) on the effect of 

 approximately linear changes of temperature have 

 been repeated using more accurate methods by 

 Hensel (42). As will be seen from figure 6, the thermal 

 sensations pass successively through all grades of sen- 

 sation from cold to warmth, although the rate of 

 change (d9/dO is kept constant. If at any stage of the 

 procedure the temperature change is allowed to stop 

 (d9/d< = o), the thermal sensation in question at 

 once becomes definitely weaker. 



With uniform rates of change of diff'erent slope the 

 time factor (adaptation) will produce a shift of the 

 threshold in such a way that the slower the rate of 

 change the more will the sensory threshold be trans- 

 ferred to the extreme regions of temperature. A 

 typical experiment is illustrated in figure 7 from 

 which it must be concluded that in the determination 

 of the thresholds for warmth and cold there must 

 exist a mutual relationship between two factors: the 

 prevalent temperature and the temporal slope (AQjAl) 

 of the intracutaneous temperature change. 



Figure 8 gives a graphical description of the mutual 

 relationship between the prevalent temperature and 

 the temporal differential quotient, d9 d/, in relation 

 to thermal .sensations. The points of the curves repre- 

 sent average values from a great number of experi- 

 ments. As will be seen, temperature changes of 

 -|-o.ooi° per sec. and —0.001° per sec. are still effec- 

 tive at temperatures above 38° and below 25°. Out- 



u 



i2 



I- 

 < 



a: so 



u 



a. 



2 



u 



^ 28 



26 



LUKEWARM 



+ 0. 45 C/MIN 



LUKEWARM 



INDIFFERENT 

 COOL 

 COLD 



.INDIFFERENT 



COOL 



0.87 °C/MIN 



COLD 



I . I . I ■ I ■ I ■ ' ■ ' ' ■ 1 



10 20 30 40 50 60 70 80 90 100 MIN 



TIME t 



FIG. 6. Course of the temperature sensation at rectilinear warming and cooling of the foot in an 

 ultrathermostate according to Hoppler. [From Hensel (45).] 



