186 THE SPECIAL SENSES. 



finger, and then roll a marble, or some small object, upon 

 the tips of the fingers (see Fig. 45), the impression will be 

 that two marbles are felt. If the fingers, thus transposed, 

 be applied to the end of the tongue, two tongues will be 

 felt. When the nose is accidentally destroyed, the surgeon 

 sometimes performs an operation for the purpose of form- 

 ing a new one, by transplanting a partially removed piece 

 of the skin of the forehead upon the injured part : then, if 

 the new nose be touched or pinched, the feeling is referred 

 to the forehead. This fact illustrates one important truth, 

 that the nerves will re-unite after they have been cut, and 

 feeling will be restored : if it were otherwise, a succession 

 of slight cuts upon the fingers would seriously impair their 

 tactile sensibility. 



24. The Delicacy of Touch. Although the hand 

 is the proper organ of this sense, yet it is exercised by 

 various parts of the body, their degree of sensibility being 

 proportional to the number of papillae they contain. The 

 varying degrees of tactile delicacy of the different parts of 

 the surface have been measured, in an ingenious manner, 

 by means of a pair of compasses, tipped with small pieces 

 of cork. The two points of the compasses are touched at 

 the same moment to the skin, the eyes being closed, and it 

 is found that, in sensitive parts, the distance between the 

 points maybe quite slight, and yet each be plainly felt; 

 while, in less sensitive parts, the points of the compasses 

 are felt as a single point, although they are separated one 

 or two inches. 



25. At the tips of the fingers, the distance between the 

 points being one-twentieth of an inch, a double impression 

 is felt. The distance must be twice as great, for the palm ; 

 four times as great, for the lips ; and, on the forehead, it 

 must be twenty times greater. At the middle of the back, 

 where the touch is least acute, the points must be sepa- 



24. The delicacy of tonch ? Experiments with a pair of compasses ? 



25. Further experiments and results ? 



