i CUTANEOUS SENSIBILITY 13 



developed by Herbart and Wundt, the first of whom specially 

 brought out the importance of association of the various sensations 

 and perceptions, while the second laid stress on the unconscious 

 reasoning processes. 



The new-born infant only possesses internal sensations, such 

 as hunger, satiety, etc. Its visual, auditory, tactile and other 

 sensations are only perceived as changes of its own being, and 

 are not referred to the causes by which they are produced, nor 

 projected externally. By degrees, however, it begins to notice 

 various objects and accommodate its eyes for distant vision. 

 Simultaneously the child moves its limbs and begins to exercise 

 its cutaneous and muscular senses. Tactile sensations are at 

 first perceived as internal sensations, as obstacles to movement ; 

 but the eye perceives the movement of the hand, and the 

 coincidence of visual and tactile sensations soon leads, by an 

 unconscious process of reasoning, to the conviction that the object 

 perceived by both senses is one and the same. Apart from the 

 association of the two senses, touch alone is sufficient by un- 

 conscious judgment to teach the babe to distinguish its own body 

 from the outside world. When the hand comes in contact with 

 another sensitive point of the skin, it receives a double sensation ; 

 when, on the contrary, it touches an extraneous object, it is aware 

 of one sensation only. 



For the adequate discussion of these and other problems the 

 student must turn to text-books of psychology. Here we must 

 confine ourselves to saying that the transformation of sensations 

 into perceptions is still a wholly mysterious process, even if it 

 can reasonably be said- to depend on and be favoured by the 

 combined activity of all the senses. 



IV. The whole surface of the skin and the visible parts of 

 the mucous membrane have important sensory functions which 

 have long been grouped together under the common denomination 

 of " tactile sensation," without regard to analysis of the different 

 qualities of sensation. For this reason, perhaps, the study of 

 these functions remained stationary for a long time, down to the 

 last decades of the nineteenth century, when a conspicuous 

 advance was made. 



Pechlin (1691) was the first who insisted on the anatomo- 

 physiological distinction between tactile and thermal sensibility 

 (caloris et frigoris sensus). Erasmus Darwin (1794), in his 

 famous Zoonomia, proposed the same distinction, and adduced" as 

 evidence the case of a patient suffering from abolition of tactile 

 sensibility, in whom the appreciation of warmth was normal. 

 But this attempt to distinguish between the different cutaneous 

 sensations was neglected until E. H. Weber (1834) undertook 

 the systematic study of the physiology of cutaneous sensibility, 

 and, after prolonged original and methodical research, obtained 



