816 FEELING AND TOUCH. 



the sensations of pressure and temperature. When each stimulus is brought 

 to bear on a very limited area, the two sensations are frequently confounded, 

 especially in those regions of the body where sensations are not acute. So, 

 also, a penny cooled down nearly to zero, and placed on the forehead will 

 be judged by most people to be as heavy or even heavier than two pennies 

 of the temperature of the forehead itself; and, conversely, a body warmer 

 than the skin will often appear heavier than a body of the same weight, but 

 of the same temperature as the skin. Moreover, cases have been recorded 

 where a hot body, such as a heated spoon, was felt, though the application of 

 the same spoon at the temperature of the body produced no sensations, and 

 yet the heated spoon was not recognized as a hot body, but appeared to be 

 simply something touching the skin. It may be argued that these instances 

 show nothing more than the changes in the skin, whatever they be, which 

 give rise to sensations of pressure, are modified by the temperature of the 

 skin for the time being, whereby the judgment as to the pressure which is 

 being exerted is rendered faulty ; but they may also be taken to indicate 

 that variations in pressure and temperature affect the same terminal organs, 

 and the same nerve-fibres, though affecting them in a different way, and 

 generating nervous impulses so far different that they give rise to different 

 sensations. And we may here note that we certainly cannot speak of nerves 

 of warmth in the same sense in which we speak of nerves of sight or of 

 hearing. A stimulus (of whatever kind) applied to an optic or auditory 

 nerve, if adequate, gives rise, as we have seen, to a sensation of light or of 

 sound ; a stimulus, on the other hand, applied to the trunk of a cutaneous 

 nerve, gives rise only to general feeling or pain ; though the nerve certainly 

 contains fibres by which sensations of pressure and of temperature reach the 

 brain, the general feeling which stimulation of the trunk causes is akin 

 neither to sensations of pressure nor to those of warmth. 



745. The rapidity with which hot or cold bodies brought into contact 

 with the skin give rise to sensations of temperature, suggests that the ter- 

 minal apparatus for generating these sensations, whatever be its nature, is 

 placed in the epidermis, and indeed as near as possible to the surface. Pres- 

 sure, on the other hand, can be readily transmitted through even a thick 

 layer of skin. And those who maintain the existence of different terminal 

 organs for pressure and temperature, regard the nerve-endings in the epider- 

 mis as the latter, and the corpuscular tactus, end-bulbs, and allied organs as 

 the former. But the evidence we possess concerning this matter is at present 

 inconclusive. 



TACTILE PERCEPTIONS AND JUDGMENTS. 



746. When a body presses on any part of our skin, or when the 

 temperature of the skin at that point is raised, we are not only conscious of 

 pressure or of heat, but perceive that a particular part of our body has been 

 touched or heated. We refer the sensations to their place of origin, and we 

 thus by touch perceive the relations to ourselves of the body which gives 

 rise to the tactile sensations, in the same way as in our visual perception of 

 external objects we refer to external nature the sensations originating in 

 certain parts of the retina. When we are touched on the finger and on the 

 back we refer the sensations to the finger and to the back respectively, and 

 when we are touched at two places on the same finger at the same time we 

 refer the sensations to two points of the finger. In this way we can localize 

 our sensations, and are thus assisted in perceiving the space relations of ob- 

 jects with which we come in contact. 



747. This power of localizing pressure sensations varies in different 



