CHAP, iv.] FEELING AND TOUCH. 573 



meaning, require for their production terminal organs; and the 

 chief but not exclusive organ of touch is to be found in the epider- 

 mis of the skin and certain underlying nervous structures. For 

 the developement of specific tactile sensations these terminal organs 

 are as essential as are the terminal organs of the eye for sight or of 

 the ear for hearing. Contact of the skin with a hard or with 

 a hot body gives rise to a distinct sensation, whereby we recognise 

 that we have touched a hard or a hot body. But the application of 

 either body or of any other stimulus to a nerve-trunk gives rise to 

 a sensation of general feeling only, corresponding to the simple 

 sensation of light which is produced by direct stimulation of the 

 optic nerve. We have no more tactile perception of a body which 

 is in contact with a nerve-trunk than we could have visual per- 

 ception of any luminous object, the rays proceeding from which 

 were strong enough to excite sensory impulses when directed on to 

 the optic nerve instead of on to the retina, supposing such a thing 

 to be possible. It is further characteristic of these ordinary nerves 

 of general feeling, that the sensations caused by any stimulation of 

 them beyond a certain degree develope that state of consciousness 

 which we are in the habit of speaking of as 'pain.' Putting aside 

 the general feeling which many parts of the eye possess, a very 

 strong luminous stimulation of the retina is required to produce a 

 sensation of pain, if indeed it can be at all brought about; whereas 

 a very moderate stimulation of the skin, and almost every stimu- 

 lation of an ordinary nerve-trunk, is said by us to be painful. 



Though the skin is the chief organ of touch, the mucous mem- 

 brane lining the various passages of the body also serves as an 

 instrument for the same sense, but only for a short distance from 

 the respective orifices. We can recognise hard or hot bodies with 

 our lips or mouth, but a hot liquid, when it has reached the oeso- 

 phagus or stomach, simply gives rise to a sensation of pain : we 

 cannot distinguish the sensation caused by it from the sensation 

 caused by a draught of a too acid fluid. 



From parts and tissues of the body other than the skin and the 

 portions of mucous membrane just mentioned we have obscure 

 sensations of general feeling, by which we are made vaguely 

 aware of the general condition of our body, though our judgments 

 in this matter are chiefly influenced by what we shall have to 

 speak of directly as a muscular sense. In all parts of the body, 

 however, on occasions all too frequent, this general feeling may 

 become prominent as pain. 



The stimuli which, when applied to the skin, give rise to tactile 

 perceptions are of two kinds only : (1) mechanical, that is, the con- 

 tact of bodies exerting varying degrees of pressure ; and (2) thermal, 

 i.e. the raising or lowering of the temperature of the skin by the 

 approach or contact of hot or cold bodies. We can judge of the 

 weight and of the temperature of a body, because we can, through 

 touch, perceive how much it presses when allowed to rest on 



