TOUCH. 



11C5 



potent exertion of the will to keep them in 

 activity. As we have every reason to believe 

 that all mental exertion, like muscular force, 

 involves (in our present state of being) a dis- 

 integration of the substance of its instrument 

 the brain, there is no difficulty in under- 

 standing that this disintegration, when carried 

 beyond a certain point, may excite the sense 

 of fatigue (see SLEEP), just as the " besoin 

 de respirer" is felt after we have withheld our 

 respiratory movements for a few seconds, or 

 hunger when there is a deficiency of nu- 

 tritious matter in the circulating current. It 

 has been said by Mr. Mayo, " that the frame 

 is in the completest health and condition, 

 when the internal sensations are not excited ; 

 the healthiest self-feeling being an absence 

 of all inward sensation." This, however, is 

 scarcely a sufficient account of the fact ; for, 

 in the highest condition of health, there is not 

 only an absence of all uneasy feeling, but a 

 general sense of buoyancy and resiliency, dif- 

 ficult to describe in words, which may be 

 characterised as the positive sense of well- 

 being. So, on the other hand, without any 

 positive or distinct sensation, there may be a 

 consciousness of general discomfort, which 

 has been expressively termed by the French 

 malaise. These two sensations may probably 

 be considered as originating in the condition 

 of the blood ; the first being an indication of 

 its purity, and of its perfect adaptation to the 

 wants of the system ; whilst the second would 

 seem to proceed from a slight depravation 

 of its quality, resulting not unfrequently from 

 the imperfect elimination of excretory matters, 

 such as is not sufficient in itself to constitute 

 an actual disease. 



Having thus passed in review the principal 

 manifestations of the general sensibility of 

 the body, and the conditions under which 

 they occur, we have now to proceed to the 

 investigation of the sense of touch, as exer- 

 cised by the organs specially adapted for the 

 reception of tactile impressions. 



SENSE OF TOUCH. 



Special Organs of Touch. The peculiar 

 endowments of the tegumentary surface, 

 which enable us to draw from the impres- 

 sions received through it, information of so 

 much more varied and definite a character 

 than we can derive through any of the struc- 

 tures which it invests, appear to consist prin- 

 cipally, so far as the organ itself is concerned, 

 in its greater sensibility (that is, in its greater 

 aptitude for being affected by slight impres- 

 sions), and in its greater power of commu- 

 nicating distinct impressions from points in 

 close proximity ; but a large part of our in- 

 formation is dependent upon our power of 

 giving motion to the tactile organ, and thus of 

 increasing the force and variety of the impres- 

 sions which we derive through its surface, as 

 well as of receiving impressions of an entirely 

 different kind, from the action of the muscles 

 by which that motion is given. Thus, if we 

 simply bring a solid body into contact with 

 the point of the finger, we gain but little 



information of the nature of its surface, 

 whether rough, smooth, or polished ; and we 

 can judge nothing of its form, except in regard 

 to that part of it in actual contact with the 

 fingers ; and even this is but vaguely ap- 

 preciated. This information may be rendered 

 somewhat more precise by pressing the object 

 against the finger ; as we shall then feel the 

 impression made by elevations, points, or 

 roughnesses, if they be sufficiently prominent 

 and wide apart from each other; whilst from 

 the degree of muscular force we exert, and 

 from the amount of yielding of which we are 

 conscious in the object itself, we judge of its 

 hardness, softness, elasticity, &c. But our 

 power of discrimination is immensely in- 

 creased, when we move the tactile surface on 

 the body to be examined, or vice versa ; for, 

 from the succession of impressions then made, 

 we obtain our best idea of the character 

 of the surface of the object ; whilst by the 

 combination of the tactile impressions with 

 the muscular sense, we judge of the relative 

 positions and connections of its different 

 parts, and of the form of the whole. But 

 besides this, we find that impressions may be 

 derived through the skin, which are not re- 

 ferable to a mere exaltation of its common 

 sensibility, being apparently of a different cha- 

 racter from any of which we become con- 

 scious through other structures ; such, espe- 

 cially, are sensations of temperature. Still 

 there would seem no sufficient cause for rank- 

 ing even these in a distinct category from the 

 ordinary tactile impressions ; for the feeling 

 of heat or cold does not differ more from that 

 of roughness or smoothness, than does the 

 colour of the object, as seen by the eye, from 

 its form as distinguished by the same organ. 



The different parts of the cutaneous sur- 

 face are endowed with tactile sensibility in 

 very different degrees ; and this variation 

 seems closely to correspond with the degree 

 of development of that papillary structure, 

 which may be regarded as the special organ 

 of touch, strictly so called. These papillce 

 are most elevated and numerous on the tip of 

 the tongue and the points of the fingers ; are 

 less so on the palms of the hands and the 

 soles of the feet ; are comparatively small and 

 few on the integument of the limbs, and on 

 several parts of the trunk can scarcely be dis- 

 covered at all. They are described by Messrs. 

 Todd and Bowman* as having an average 

 length in man of T ^th of an inch ; and a 

 diameter at their base, where they spring from 

 the cuticle, of about Tth of an inch. Their 



form is somewhat conical, tapering off to a 

 slightly rounded point. Their surface (after 

 the removal of the epidermis) appears to be 

 composed of the basement membrane of the 

 cutis itself ; and their interior is composed of 

 fibrous tissue, vessels, and nerves. In each 

 papilla we find a small arterial twig, derived 

 from the arterial plexus of the cutis ; this, 

 advancing towards the apex of the papilla, 

 subdivides into two or more capillary ves- 



* Physiological Anatomy, vol. i. p. 410. 



