952 CUTANEOUS SENSATIONS. 



it can cool the cutaneous end-organs. It is assumed, in consequence of 

 the results of the spatial analysis of the sensifacient surface, that 

 lowering the skin temperature does not stimulate " warmth " organs, 

 and that conversely the " cold " organs are not excited by a heightening 

 (unless very excessive) l of the skin temperature. 



The complexus of attributes (temperature, thermal conductivity, 

 specific heat, nature of surface, etc.) which combine to constitute the 

 value of an object as a " cold " stimulus when the object is of temperature 

 below the " adequate," combine to constitute its value, conversely, as a 

 " warmth " stimulus when the object is above the " adequate " tempera- 

 ture. The thermal senses are often termed " the sense of temperature," 

 and rightly, in so far that it is " temperature " which, ranging on either 

 side of the " adequate temperature " as zero, determines the species of the 

 sensation ; the other thermal qualities, such as conductivity, etc., only 

 affect the quantity or intensity of the sensation. Alteration in skin 

 temperature sufficient in speed and degree to evoke sensation, may be 

 brought about by internal as well as by external changes. Thus, a 

 flushed cheek " feels hot." 



Weber urged that the actual process of falling or rising of the 

 temperature of the cutaneous end-organ constitutes the adequate 

 stimulus for the temperature sense. Hering has, on the contrary, put 

 forward the view that the difference existing between the temperature 

 of the end-organ and a physiological zero of temperature, to which it in 

 its skin region is for the time being " adapted," constitutes the stimulus 

 for temperature sense. Vierordt suggested that the transmission of a 

 certain quantity of heat through the skin is the objective cause of all 

 temperature sensations. The direction, according to him, as well as 

 the intensity, of the transmission determines the sensation, the sensa- 

 tion, in his view, being altogether independent of the alterations of the 

 objective temperature of the skin. The fact that a " warmth " sensa- 

 tion can be produced by a sudden hypersemia of the skin, as well as by 

 a warm object applied from without, controverts Vierordt's view that 

 direction of transmission of heat determines the sensation. 



If a metal disc, a little above C., be applied to the skin, e.g. of the forehead, 

 for 30 seconds, the resulting " cold sensation " persists fully 20 seconds after 

 removal of the disc. The " cold sensation," therefore, endures while the locally 

 depressed temperature of the skin is rising ; and, conversely, after strong stimula- 

 tion by warmth. This offers a difficulty to Weber's view. Facile evocation of 

 positive after sensations is characteristic of the temperature senses; in this 

 respect both resemble the cutaneous pain sense. Further, the physical stimulus, 

 the change in temperature, not only stimulates the nerve-endings, but actually 

 alters their temperature; and if their temperature be much reduced or 

 heightened, their excitability for a fresh stimulus is lessened. The nipples are 

 exquisitely sensitive to warmth ; if one be cooled, and then to both the same 

 warm stimulus be consecutively applied, of the resultant warm sensations, that 

 evoked from the cooled nipple is not the greater but the less. 2 The finger held 

 in water at 40 C. for 10 seconds, and then, together with the dry finger of 

 the other hand, placed in water at 15 C., "feels the cold" less than does the 

 unwarmed finger. Further, if the finger of one hand (A) be held in 

 water at 32 C., and the corresponding finger of the other hand (B) be at 



1 v. Frey, loc. cit., states that from "cold-spots," by excitation with hot objects, "cold 

 sensations " can be evoked. So also S. Alriitz, Skandin. Arch. f. PhysioL, Leipzig, 1897, 

 Bd. vii. S. 321 ; F. Kiesow, Phil. Stud., Leipzig, 1898, Bd. xiv. S. 585. 



2 Goldscheider, loc. cit. 



