SENSATION. 399 



The sensibility, thus distributed over the integument, varies in 

 its acuteness in different parts of the body. Thus, the extremities 

 of the fingers are more sensitive to external impressions than the 

 general surface of the limbs and trunk. The surfaces of the fingers 

 which lie in contact with each other are more sensitive than their 

 dorsal or palmar surfaces. The point of the tongue, the lips, and 

 the orifices of most of the mucous passages are endowed with a 

 sensibility which is more acute than that of the general integument. 



If the impression to which these parts are subjected be harsh or 

 violent in its character, or of such a nature as to injure the texture 

 of the integument or its nerves, it then produces a sensation of pain. 

 It is essential to notice, however, that the sensation of pain is not 

 a mere exaggeration of ordinary sensitive impressions, but is one 

 of quite a different character, which, is superadded to the others, or 

 takes their place altogether. Just in proportion as the contact of a 

 foreign body becomes painful, our ordinary perceptions of its phy- 

 sical properties are blunted, and the sense of suffering predominates 

 over ordinary sensibility. Thus if the integument be gently touched 

 with the blade of a knife we easily feel that it is hard, cold, and 

 smooth ; but if an incision be made with it in the skin, we lose all 

 distinct perception of these qualities, and feel only the suffering 

 produced by the incision. We perceive, also, the difference in 

 temperature between cold and warm substances brought in contact 

 with the skin, so long as this difference is moderate in degree ; but 

 if a foreign body be excessively cold or excessively hot, we can 

 no longer appreciate its temperature by the touch, but only its 

 injurious and destructive effect. Thus the sensation caused by 

 touching frozen carbonic acid is the same with that produced by a 

 red-hot metal. Both substances blister the surface, but their actual 

 temperatures cannot be distinguished. 



It is, therefore, a very important fact in this connection, that the 

 sensibility to pain is distinct from the power of ordinary serration. This 

 distinction was first fully established by M. Beau, of Paris, who has 

 shown conclusively that the sensibility to pain may be diminished 

 or suspended, while ordinary sensation remains. This is often seen 

 in patients who are partially under the influence of ether or chlo- 

 roform. The etherization may be carried to such an extent that 

 the patient may be quite insensible to the pain of a surgical opera- 

 tion, and yet remain perfectly conscious, and even capable of feeling 

 the incisions, ligatures, &c., though he does not suffer from them. 

 It not unfrequently happens, also, when opium has been adminis- 



