396 



ON SENSATION, AND THE ORGANS OF THE SENSES. 



Fig. 162. 



Capillary net-work at margin of 

 lips. 



by the aid of a lens, and each chiefly composed of a vascular loop overlapping 



the extremity of the nervous fibril. The pre- 

 cise arrangement of the nerve-fibres in the cuta- 

 neous papillae, has not been indisputably ascer- 

 tained ; but the opinion that they form loops 

 (Fig. 119) is the one most generally adopted. 

 The number of these papillae within any given 

 area, pretty closely corresponds with the degree 

 of sensibility of that part of the surface ; thus 

 we find them most abundant on the hands, es- 

 pecially towards the points of the fingers, and 

 on the lips and tongue. In some animals, es- 

 pecially those of the Feline tribe, the long vi- 

 brissse (commonly termed whiskers) evidently 

 minister to sensation; and it has been demonstrated that their pulps are 

 largely supplied with nerves from the fifth pair. Some interesting observa- 

 tions have been made by Prof. Weber, on the sensibility of different parts of 

 the skin. His mode of ascertaining this, was to touch the surface with the 

 legs of a pair of compasses, the points of which were guarded with pieces of 

 cork ; the eyes being closed at the time, the legs were approximated to each 

 other, until they were brought within the smallest distance, at which they 

 could be felt to be distinct from one another. The following are some of the 

 results of the experiments. With the extremities of the fingers and the 

 point of the tongue, the distance could be distinguished most easily in the 

 longitudinal direction ; on the dorsum of the tongue, the face, neck, and ex- 

 tremities, the distance could be recognized best when the points were placed 

 transversely. 



5 of a line 

 tj of a line 

 1 line 



Point of middle finger . 

 Point of tongue 



Palmar surface of third finger 



Red surface of lips . . 2 lines 



Palmar surface of middle finger 2 



Dorsal surface of third finger 3 



Tip of the nose ... 3 



Dorsum and edge of tongue 4 



Part of lips covered by skin 4 



Palm of hand ... 5 



Skin of cheek ... 5 



Extremity of great toe . . 5 



Hard palate ... 6 



Dorsal surface of forefinger . 7 



Dorsum of hand , 8 



Mucous Membrane of gums 

 Lower part of forehead . 

 Lower part of occiput 

 Back of hand . 

 Neck, under lower jaw . 

 Vertex .... 

 Skin over Patella 

 Sacrum 



acromion 



Dorsum of foot 

 Skin over sternum . 

 Skin beneath occiput 

 Skin over spine, in back 

 Middje of the arm . 

 thigh 



9 lines 



10 



12 



14 



15 



15 



16 

 18 

 18 

 18 

 20 

 24 

 30 

 30 

 30 



It is curious that the distance between the legs of the compasses seemed to 

 be greater (although really so much less), when it was felt by the more sensi- 

 tive parts, than when it was estimated by parts of less distinct sensibility. As 

 a general fact, it seems that the sensibility of the trunk is greater on the me- 

 dian line, both before and behind, and less at the sides. Differences of tem- 

 perature, and the weight of bodies, were, according to Prof. Weber's observa- 

 tions, most accurately recognized at the parts, which were determined to be 

 most sensible by the foregoing method of inquiry. 



523. As already stated( 514), the only idea communicated to our minds by 

 the sense of Touch, when exercised in its simplest form, is that of Resistance; 

 but when the sensory surface and the substance touched are made to change 

 their place in regard to each other, we obtain the additional notion of Extension 

 or Space. By the various degrees of resistance which the sensory surface 

 encounters, we estimate the hardness or softness of the body; but in this we 



