THE SKIN AND COMMON SENSATION. 965 



another ; and Weber showed that such stimuli, when applied to surfaces near 

 together, mutually reinforce one another more than when farther apart. 



Antagonism of sensations of "cold" and "warmth." If by the 

 thermo-resthesiometer a sensory circle for cold or warmth has been 

 carefully delimited, and if then two fairly equal thermal stimuli, one 

 cold, one hot, be simultaneously applied within the limits of the circle, 

 a curious sensation results. Czermak, who performed the experiment 

 with use of small test-tubes filled with oil and warmed or cooled, says, 

 " one then distinguishes the sensation due to the cold test-tube quite 

 clearly from that due to the warmed ; but, owing to there being no hint 

 of the relative neighbourhood of the two, one is thrown into a peculiar 

 and indescribable confusion," which only disappears when the distance 

 between the two stimuli is sufficiently increased. Klug, using 

 Kronecker's fine-pointed thermo-sesthesiometers, found the average 

 liminal distance not diminished by making one cold, the other warm. 

 When the two points lay at less than that distance, he felt a duplex 

 sensation, but of temporal, not of spatial duplicity. He describes the 

 sensation as alternating cold and warmth, in fact, resembling the 

 sensation obtained by presenting different colours to identical areas of 

 the two retinae simultaneously. 



Paths of conduction. The facts mentioned above make it more than 

 probable that the afferent nerve fibres for " cold " and for " warmth " 

 respectively are distinct. The same conclusion is supported by patho- 

 logical evidence. Herzen l found, in experiments on the cat, that after 

 transection of the dorsal spinal white column, the foot on the side of 

 the lesion was not withdrawn when a piece of ice was applied to it, 

 although the animal at once withdrew its opposite foot from contact 

 with a similar stimulus. 2 



The sundering of the species of cutaneous sensations one from another in 

 spinal disease most frequently takes the form of partial, often severe, impart- 

 ment of pain and thermal sense, while touch remains intact. It used to be said 

 that in disturbance of cutaneous sense the thermal sensations were the last and 

 least to suffer. Goldscheider 3 declares that rather the reverse is true. In 

 tabes, syringomyelia, neuritis, etc., it is not very uncommon to find dis- 

 tinction drawn by the disease between sensations of cold and warmth, the one 

 failing, the other not. Isolated impairment of "warmth" is more common 

 than of "cold." 4 Certainly the effect of drugs upon skin sensitivity has 

 marked effects on the thermal elements. 



THE SKIN AND COMMON SENSATION. 



The skin contributes, as might be expected, to so-called " common 

 sensation." Its contributions are especially characteristic in certain 

 pains, sexual feelings, the " feelings " of tickling, shivering, shuddering, 

 and the like. From no part of the body can pain more urgent be pro- 

 voked than from the skin. A question, arising almost necessarily at 

 the outset in dealing with the physiology of cutaneous pain, regards the 

 relation between it and other sensations of cutaneous origin. Is cutaneous 

 pain the product of a specific sense of pain ? Data for complete satis- 

 faction of this problem seem still insufficient. It is necessary, in order 



1 Arch.f. d. ges. Physiol., Bonn, 1866, Bd. xxxvii. 



2 The conduction paths for thermal sensations are referred to in the article "Spinal 

 Cord," p. 866. 



3 Loc. tit. 4 Schlesinger, "Die Syringomyelia," Wien, 1895. 



