HALLUCINATIONS. 367 



internal causes ; thus, the sensations of formication, creeping, or ting- 

 ling, may arise independently of external influences : such tactile sen- 

 sations are of frequent occurrence. 



The sense of touch is capable of being educated, as is well seen 

 amongst the blind, whose tactile discrimination is so acute and deli- 

 cate, that they are able to read sentences in raised letters, to distin- 

 guish the inscriptions and impressions on coins, and frequently even 

 to recognize shades of color, which escape the notice of the eye, by 

 means of differences of texture and surface. It has been found that 

 the sense of space or locality, as determined by experiments with the 

 compasses, or with the aethesiometer, is well developed in the case of 

 blind persons, not only in the hands, but even in all the other parts 

 of the body. In persons born without arms, the sense of touch in the 

 toes sometimes becomes, by dint of education, so highly developed, 

 that these can be used in the same manner as the fingers. The in- 

 fluence of habit, in improving the delicacy of the tactile sense, is illus- 

 trated by the mode in which factory girls can detect and join the 

 finest fibres of silk and cotton, in the spinning machines. The Ben- 

 galee female silk-throwsters are said to be able to distinguish by the 

 touch as many as twenty different degrees of fineness in the fibres of 

 the cocoons. It has even been alleged, in regard to the influence of 

 education on the tactile sense, that an improvement, in this respect, 

 in any part, on one side of the body, is accompanied by a correspond- 

 ing improvement in the same part of the body on the opposite side. 



Hallucinations connected with the sense of touch are not un- 

 common. A familiar example is that afforded by crossing two fingers 

 of the same hand, and rolling between them a small rounded body, 

 such as a pea, when the sensation of a double body is experienced. If 

 the point of one's tongue be so touched, two tongues are felt. A stick 

 pressed simultaneously against the upper and lower lip, appears to be 

 straight, but if one lip be moved sideways, or if both be moved in 

 opposite directions, the stick seems to be broken ; if this experiment 

 is performed before a looking-glass, the illusion is at once dispelled. 

 (Czermak.) If a body, such as a ball, be touched with sticks of dif- 

 ferent lengths, whilst the eyes are turned in another direction, it will 

 be found that, when the sticks are carried round the body, this appears 

 smaller the greater the length of the stick, the angle which is then 

 described being much smaller. These are errors of judgment, based 

 on sensations with which we are not familiar. In transplantation of a 

 portion of skin from one part to another, as in the formation of a new 

 nose by a flap of skin turned down from the forehead, but still left 

 connected with that part, by a narrow bridge of integument, the sen- 

 sations are, for a time, referred to their old seat ; so that, when the 

 new -formed nose is touched, the sensation is felt as if it were in the 

 forehead. This is the case, however, only so long as the nerves in the 

 connecting bridge of skin are undivided, and it is uncertain whether 

 the mistake can be corrected by the aid of vision. If the connecting 

 nerves are cut through, all sensibility is temporarily lost in the new 

 nose, until, after a time, new nerves enter it through the cicatrix. 



