NEEVES OF THE PAPILLA. 421 



shown by examinations with a fine needle. At first he ,, 



Jbvery part of 



thought he had found some places which were quite insensi- the skin is sen- 

 ble, while in others the slightest touch produced sensation ; 8Itlve * 

 but on carrying the investigation farther, it appeared that the very same 

 place was sometimes sensible and sometimes not, so that finally he came 

 to the conclusion that the very smallest portions of the skin are sensi- 

 tive. But since, even in the palm of the hand, the papillae containing 

 nerves are widely dispersed, and in other places occur but rarely, or 

 even not at all, he infers that it is necessary to assume the existence of 

 non-medullated fibres in all the papillae, or to have recourse to the nerv- 

 ous plexus at their base, since he believes it is not possible to demon- 

 strate nerves in eveiy one of those bodies. 



The nerves supplying the papillae may perhaps be said to ascend 

 through the cutis, continually branching, and forming eventu- papillary 

 ally terminal plexuses. The primitive tubules themselves di- nerves. 

 viding at an acute angle into two, and entering the papillae, they are 

 united at their extremities in a loop. Of course, this construction in- 

 volves the fact that they have freed themselves from the white substance 

 of Schwann. The impression made on these exposed nervous fibrils is 

 by many regarded as of a purely mechanical kind. They may be affect- 

 ed not merely by vertical pressures, but likewise by those exerted in the 

 direction of the plane of the skin, and this accounts for tactile sensation 

 on portions of that surface which are either sparsely or not at all sup- 

 plied with nerve fibrils. To this effect the unyielding and horny texture 

 of the cuticle doubtless contributes. 



No papillae are found in invertebrate animals. Among vertebrates 

 they are variously disposed. In lizards they occur under TQ^ j n other 

 the toes ; in the chameleon, and some of the ant-eaters, which vertebrates. 

 use their tails for tactile purposes, they are found upon that organ. In 

 the spring season of the year they are temporarily developed on the thumb 

 of the frog. Among birds they are found upon the toes, or, if web-foot- 

 ed, upon the web ; in the mole on the tip of the snout. In the tapir and 

 elephant they occur upon the trunk ; among the quadrumana, on the 

 hands and feet, and in some also upon the tail. The whiskers of the cat, 

 the rat, the rabbit, may be regarded as appendages to the tactile organs, 

 enabling them to find their way through narrow passages in the dark. 

 Among articulata the antennae have doubtless, with their other functions, 

 a similar use. Men who have become blind often guide their steps by 

 means of a stick, judging from the sensations which its contact with sur- 

 rounding bodies imparts to the hand : it is in all respects a temporary 

 antenna. 



Our estimates of the hardness and softness, roughness and smoothness 

 of bodies, is primarily dependent on indications derived from the sense 



