858 OF SENSATION, AND THE ORGANS OF THE SENSES. 



pain; and in cutting off the sleeve, he frequently cried out; yet when the arm 

 was exposed, it was found to be quite uninjured, the hook having only traversed 

 the sleeve of his coat !" In this and similar cases, the sensation was perfectly 

 real to the individual who experienced it ; but it originated in a Cerebral 

 (ideational) change which produced its impression through the nerves of internal 

 sensation ( 758), instead of in an impression upon the nerves of the external 

 senses to which it was referred. Of this kind of action we have seen other 

 examples, in the production of sensations by " suggestion" in the state of arti- 

 ficial reverie ( 825). And the excitement of the peculiar sensation of tickling 

 in a ticklish person by any movement that suggests the idea, and of that of 

 creeping or itching by the mention of bed-infesting insects to those who are 

 peculiarly liable to their attacks, are familiar instances of the same fact ; which 

 strongly confirms the general doctrines heretofore advanced, respecting the 

 analogy between the peripheral surface of the Cerebrum and the peripheral 

 expansions of the Sensory nerves, as regards their mutual relations to the Sen- 

 sorium ( 753). 



2. Sense of Touch. 



864. By the sense of Touch, as commonly understood, is meant that modi- 

 fication of the common sensibility of the body, of which the cutaneous surface 

 is the especial seat. The Skin is peculiarly adapted for this purpose, not merely 

 by the large amount of sensory nervous fibres which are distributed in its sub- 

 stance, but also by its possession of a papillary apparatus in which these nerves 

 terminate, or rather commence. The papillse are little elevations of the surface 

 of the cutis, easily perceptible by the aid of a lens ; each is chiefly composed 

 of a vascular loop (Fig. 196), in close relation with a similar loop formed by 

 the nervous fibril ; and also incloses (as appears from the recent researches of 

 Professors Wagner and Kblliker) an "axile body," composed of a mass of 

 homogeneous areolar tissue with an external layer of imperfectly developed 

 elastic tissue, and essentially similar to the bundles of fibrous tissue encircled 

 by elastic fibres which are to be found in the cutis. These " axile bodies" are 

 only to be found in the papillae of those parts which are distinguished for acute- 

 ness of tactile sensibility; and hence we cannot regard them as essential to the 

 exercise of the sense of touch, their function probably being to intensify tactile 



impressions, where delicacy of touch is peculiarly 

 Fig. 196. required. 1 The number of these papillae within 



any given area pretty closely corresponds with 

 the degree of sensibility of that part of the sur- 

 face; thus we find them most abundant on the 

 hands, especially towards the points of the fingers, 

 and on the lips and tongue. Some interesting 

 observations 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 

 Capillary network at margin of lips, 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, which has been 



1 The accounts of the structure of the tactile papillse given by Prof. Kolliker in his 

 " Mikroskopische Anatomic," band ii. p. 24, and in the " Zeitschrift fur Wissenschaften 

 Zoologie," band iv. heft 1, 1852, are here followed. For a notice of the peculiar views of 

 Prof. Wagner, see the "Brit, and For. Med.-Chir. Rev.," vol. x. p. 251 [or \ 343 ED.]. 



