i CUTANEOUS SENSIBILITY 53 



forehead the slightest touch will arouse tickling and a desire 

 to scratch to remove the annoyance. In these parts it is not 

 necessary to excite with light and delicate stimuli ; coarse 

 mechanical stimulation will arouse such a tickling that it causes 

 violent reflex movements spreading to almost all the muscles, and 

 uncontrollable by the will. 



The sensation of itching which accompanies different cutaneous 

 diseases is normally produced by the sting of an insect, and may 

 readily be aroused by the prick of a fine needle. But Jessner 

 holds, on the contrary, that itching is a paraesthesia, i.e. a morbid 

 variety of cutaneous sensibility that is absent in normal individuals. 



There is no very marked difference between the sensations of 

 tickling and itching; there are intermediate sensations, which 

 may be regarded as mixed sensations, due to the simultaneous 

 excitation of several sense-organs. 



According to Weber, tickling depends on a diffusion of the 

 excitation, and on the persistence and increase of the sensation 

 after the stimulation has ceased. Funke, too, regards tickling as 

 a secondary effect of sensations of contact, which only arises on 

 applying weak stimuli. Goldscheider, who, as we saw, ascribed 

 pain sensibility to the pressure end-organ, refers tickling also to 

 a special mode of excitation of the same organ. .Von Frey and 

 Kiesow, on the contrary, hold the organs for pressure and pain 

 to be distinct, and refer the sensation of tickling to the first, of 

 itching to the second. With Quincke they regard tickling and 

 itching not as primary, but as secondary sensations, caused by 

 reflexes acting from the nerves of touch and pain upon the vaso- 

 motor nerves. But on what does the peculiar feeling of these 

 sensations depend ? Why do they arise with weak stimulation 

 and disappear when the stimulus is strengthened ? These 

 questions are unsolved. 



Alrutz has disputed the theory of v. Frey and Kiesow. He 

 considers that tickling and itching are two varieties of a single 

 modality of sensation, depending on special nerves other than 

 those of pressure and pain. He states that the sensation of 

 tickling is produced by excitation of cutaneous spots other than 

 the touch and pain spots. He quotes a case of lead-poisoning 

 described by Bean, in which there was analgesia without disturb- 

 ance of pressure sensibility, but with insensibility to tickling. In 

 two other cases of circumscribed or diffuse analgesia he observed. 

 the same state, that is, persistence of tactile sensibility in parts 

 insensitive to tickling. He further cites a case of hyperalgesia 

 communicated by Goldscheider in which there was hyperaesthesia 

 for sensations of tickling and itching. These must accordingly 

 run parallel with the pain sense and not with tactile sensibility. 



It remains for further researches to decide which of these 

 opposing theories is correct. 



