TOUCH SPOTS. 



921 



further refinement, the individual 

 fields may be reduced to mere " spots." 

 Each of these " spots " is found to 

 subserve a specific sense, — touch, cold, 

 warmth, or cutaneous pain. Each 

 doubtless coincides with the site of 

 some sensorial "end-organ," or with 

 a tiny cluster of such. Rather, 

 indeed, than to a mosaic may the 

 skin be likened to a sheet of water 

 wherein grow water - plants, some 

 sunken and some floating. An object 

 thrown upon the surface moves 

 the foliage commensurately with 

 the violence of its impact, its di- 

 mensions, and with their propinquity 

 to its place of incidence. Where 

 the foliage grows densely, not a 

 pebble striking the surface but will 

 meet some leaf ; and beyond that 

 or those directly struck, a number 

 will lie indirectly disturbed before 

 equilibrium of the surface is re- 

 established. 



Throughout almost all regions of 

 the skin " touch spots," " cold spots," 

 " warmth spots," and " pain spots " 

 lie strewn in intercommingled 

 fashion. In some districts one variety 

 predominates, in other districts 

 another. On the whole, " pain spots " 

 seem to be the most numerous, and 

 certainly " warmth spots " are the 

 least so. 



Touch. 



Touch means, in physiology, a 

 sensation evoked, under normal con- 

 ditions, by mechanical stimulation 

 from the skin ; under abnormal condi- 

 tions it may also be evoked by a 

 variety of other stimuli. 



Touch spots. — If in an area of 

 the skin, e.g. of the calf, the hairlets 

 be cut short, and the surface minutely 

 tested from point to point by 

 pressing on it perpendicularly a 

 bristle, a certain number of spots are 

 found, at which the slight pressure 

 employed (about 33 grms. on the 

 square millimetre, applied to an area 

 equal to the cross-section of a fine 



Fig. 368. — Map showing the relative 

 distribution of the sensitivity to 

 touch, warmth, and cold in the 

 palm of the left hand. In A the 

 whole surface is, when tested by a 

 small cork applied by a spring, 

 found of approximately equal sensi- 

 tivity except in the areas marked 

 black ; these are relatively insen- 

 tient for touch. In B the areas of 

 sensitivity to warmth stimuli are re- 

 presented by degrees of shading, the 

 most sensitive by the black shading, 

 the next by the lined areas, the next 

 by the dotted areas, and those of 

 least sensitiveness by the blank 

 spaces. In C the topography of the 

 distribution of sensitivity to cold 

 stimuli is indicated in the same 

 way as that to warm stimuli in 

 B. — From Goldscheider. 



