742 SPECIAL SOMATIC AND VISCERAL RECEPTORS 



in the area immediately adjoining. Quite similarly, the mapping out 

 of the surface with a thermaesthesiometer through which cool water 

 is made to flow, yields sensations of cold within fields of no thermal 

 stimulation. It appears, therefore, that the integument embraces 

 a series of warm and cold points which when properly marked in dif- 

 ferent colors, will be seen to occupy dissimilar areas. The cold spots 

 are more numerous than the warm spots, their relationship being as 

 13 : 1.5. In between these positive fields we have areas which do not 

 give rise to a distinct temperature sensation and are, therefore, called 

 indifferent fields. But these temperature points are not confined to the 

 skin alone but are also disseminated through the mucous membranes 

 of the mouth, nose, external auditory meatus, and anus.^ 



Cold spots. Heatspots. 



Fig. 369. — Heat and Cold Spots on Part of Palm of Right Hand. 

 The sensitive points are shaded, the black being more sensitive than the lined, and 

 these more sensitive than the dotted parts. The unshaded areas correspond to those 

 areas in which no special sensation was evoked. (Goldscheider.) 



The acuteness of the temperature sense varies in different regions 

 of the body. Thus, it has been observed that the areas situated in 

 the midline of the trunk, are less sensitive than those situated more 

 laterally, and that the left side, in general, is more sensitive than the 

 right. 2 The lateral aspects of the extremities are relatively insensi- 

 tive. The same holds true of the mucous surfaces, when compared 

 with the skin. Inasmuch as the latent period is shortest in the case 

 of the cold points, the stimulation of a certain area of the integument 

 most generally elicits the sensation of cold before that of heat. More- 

 over, the former sensation develops more rapidly than the latter and 

 seems, therefore, to be the more intense. Much depends, of course, 

 upon the size of the area stimulated. Thus, a finger immersed in 

 water of a certain temperature always gives a more moderate sensation 

 than the entire hand. 



Von Frey believes that the sensation of cold is mediated by the 

 corpuscles of Krause. The activation of these endings may also be 



1 Zeitschr. fiir Biol., xx, 1884, 141 ; also Goldscheider, Uber denSchmerz, Berlin, 

 1894, and Gesellsch. Abhandlungen, Leipzig, 1898. 



2 E. H. Weber, Wagner's Handworterbuch der Physiol., iii, 544. 



