80 INTRODUCTION TO NEUROLOGY 



but there is no discrimination of two compass points applied simultaneously 

 to the overlying skin. The two points will appear as one stimulus, even 

 when widely separated. 



The cutaneous organs of tactile sensibility are of several kinds, whose 

 precise functions are still obscure. There are two principal groups of these, 

 those arranged in the hair bulbs at the roots of the hairs and those on the 

 hairless parts, such as the lips, the palms of the hands, and the soles of the 

 feet. The latter are more highly differentiated endings and are organs of 

 the most refined active touch. 



Most of the surface of the body is more or less hairy, though many of 

 these hairs may be so fine as to escape observation. The hairs are the most 



Fig. 22. Pacinian corpuscles from the peritoneum of a cat. (After Sala, 

 from Bohm-Davidoff-Huber's Histology.) 



important sources of excitation of the first group of cutaneous sense organs, 

 and the sensitiveness of the hair-clad parts is greatly reduced after the hair 

 is shaved. The threshold of excitation to touch of the skin about the base 

 of a hair is from three to twelve times higher than that of a similar excita- 

 tion applied to the hair itself. The inneryation of the hair bulbs is very 

 complex and varies greatly for different animals and for the different kinds 

 of hairs on the same body, so that no general description is possible. 



Miss Vincent has shown that the large vibrissse of the rat receive their 

 nerve-supply from two sources. A large nerve bundle pierces the deep 



