TOUCH, PRESSURE, AND LOCATION 



355 



Some of these are found in the body's interior, but in small numbers. 

 Many regions of the viscera are quite devoid of touch-sensation. 



All these kinds of end-organs are probably connected by special 

 nerve-fibrils to the cord. The impulses pass up by columns and to 

 centers already described, and may stop in the posterior frontal 

 convolutions, but it is unlikely that these kinds of sensation have 

 any sharply defined areas of cerebral representation. 



FIG. 206 



FIG. 207 





Tactile disks from the epithelium of the pig's 

 snout: mk, the tactile disks; z, epithelial wall; 

 n, nerve. (Tretjakoff.) 



TOUCH-SPOTS. Goldscheider in 

 1884 showed that the skin is dotted 

 with minute areas each of which 

 possesses a sort of sensation pecu- 

 liar to itself touch, heat, cold, or 

 pain (see below). There is still 

 more or less disagreement as to the 

 arrangement of these "spots," but as 

 later study shows that these areas 

 may be reduced to mere spots, each 

 is undoubtedly some one of the end- 

 organs just described. On running 

 a needle ground especially fine into 

 one of these spots no suggestion of 

 pain (nor of warmth nor of cold) is 



felt, but a strong, sharply localized sensation of pressure unaccom- 

 panied by any other sensation than that of its relative location on or 

 in the body. Almost always there are one or more touch-spots close 

 to a hair, usually on the side from which the hair slopes, and they also 

 are apt to be arranged in certain regions in short lines radiating from 

 the hair-follicles. Where no hairs exist the arrangement of the spots 

 is the same. 



Certain Tactual Qualities. It is plain that the large variety of the touch- 

 pressure-location end-organs noted above suggest a like number of 



The nerve-ring (of Bonnet) about 

 hair of a dog: a and 6, begin to ascend the 

 longitudinal fibrils, while at c the circular 

 fibrils may be seen. (Probably the most sen- 

 sitive of the touch end-organs). (Bonnet.) 



