CUTANEOUS SENSIBILITY 



15 



pleasure, etc., or whether these should be considered as special 

 modifications of the senses of touch and pain. 



A clear idea of the form, arrangement, and number of the 

 different sensory points on the skin may be obtained by briefly 

 reviewing the experiments on which the discoveries of 

 Blix, Goldscheider, and v. Frey were founded. 



The simplest apparatus will serve for investigating heat and 

 cold spots. Small metal rods with blunt ends, that can be 

 dipped into cold or hot water, would be suitable, except that 

 they have to be changed so frequently, and that it is impossible 

 to be certain that they always act on the skin at uniform 

 temperature. The contrivance of Blix, which consists in a 

 small hollow metal cylinder, through which flows a constant 

 stream of water at uniform temperature, is more reliable. 

 Alrutz and Kiesow made various alterations in this apparatus, 

 so that it can be used for different purposes. The most perfect 

 is the thermo-aesthesiometer of Veress (Fig. 1), which is used for 

 mapping out the. thermal sensibility of small cutaneous areas 

 of 2 or 6 mm. The end of the apparatus can be unscrewed and 

 readily replaced by surfaces of different sizes, or by a blunt 

 point, when required for the investigation of heat spots. 



For pressure points the simplest and easiest method is that 

 of v. Frey with the so-called exploring hairs or bristles. Hairs 

 of varying thickness (horse-hair, woman's hair) are fixed to the 

 end of a rod, the length of which varies from 1 to 4 cm. Fig. 2 

 gives the latest form of v. Frey's hair-aesthesiometer. The 

 anterior graduated half of the metal cannula runs backwards 

 and forwards, so that more or less of the hair is covered. If the 

 point of the hair is placed on, and vertically pressed against, 

 the scale-pan of the balance, the amount of pressure necessary 

 to bend it lightly can be determined ; this, of course, increases 

 or diminishes according as the length of the hair is less or 

 greater. The millimetre scale of the instrument serves for the 

 empirical graduation of the degree of pressure required to bend 

 the hair according to the length of the exposed portion. 



The same aesthesiometer may be used to determine pain 

 points if the exposed portion of the hair is so short that it will 

 bend only at a pressure sufficient to evoke a sensation of pricking. 



If a moderately cool metal point is brought into 

 contact with the skin, without pressure, the sensation 

 of cold is evoked only at circumscribed spots, distant 

 1-2 mm. from each other. These are the cold spots of 

 Blix. If the metal point used for exploring the skin is 

 much cooled, a sensation of cold can also be obtained 

 from other surrounding areas of the skin ; but it is 

 always less intense, proving that it depends on transmission of 

 the stimulus to the true cold spots. If the skin is tested with a 

 hot metal point, sensitive spots are found which react in the same 

 way by sensations of warmth. These are the heat spots of Blix. 

 Exploration of the skin with gentle tactile stimuli, as by hairs, 

 gives Blix' pressure spots. Finally, the same method will detect 

 v. Frey's pain spots. 



FIG. 2. Hah- 

 aesthesio- 

 meter of v. 

 Frey. Epc- 

 planation in 

 text. 



