842 ^4^ AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



sphere of carbon dioxide surrounding an area of skin gives a sensation of 

 warmth. 1 



The specific difference of the two sets of temperature nerves is indicated by 

 the fact that when a warm and a cold body held close together are simulta- 

 neously brought near the skin, the sensation is either one of both warmth and 

 cold, or now one and now the other sensation predominates. 2 Any stimulation, 

 whether mechanical or electrical, applied to the sensitive points thus far de- 

 scribed in the skin, for the appreciation of either pressure, heat, or cold, pro- 

 vokes, when effective, only the proper sensation of that point ; any irritation 

 of a cold, hot, or pressure point gives rise, respectively, to the sensation of 

 cold, heat, or pressure alone. 



As in other organs of special sense, the peripheral terminations of the 

 temperature nerves seem modified to be especially irritable toward their appro- 

 priate form of physical stimulus. Cold or heat directly applied to the nerve- 

 trunk excites no temperature sensation. Thus, if the elbow be dipped into a 

 freezing mixture, as the lowered temperature penetrates to the ulnar nerve the 

 sensation will be one, not of cold, but of dull pain, and it will be referred to 

 the hand and the fingers. The internal mucous surfaces of the body, from 

 the ossophagus to the rectum, inclusive, have no power of discriminating 

 temperature sensations ; a clyster of water cooled to from 7 to 16 C., if not 

 held too long, is only perceived as cold when the water escapes through the 

 skin of the anus. 



The doctrine of specific nerve energy, enunciated by E. H. Weber, was 

 intended to convey the idea elaborated above, that each nerve of special sense, 

 however irritated, gives rise to its own peculiar quality of sensation. But it 

 seems clear that the existence and quality of the sensation are, respectively, 

 properties of the activity, not of the nerve-fibre, but of the peripheral end- 

 organ and the nerve-centres. 



3. Common Sensation and Pain. The sensations thus far considered 

 have been called special sensations, because each affects the consciousness in 

 quite a different way, and any irritation which excites the sense apparatus 

 provokes a sensation of definite quality and measurable intensity. 



Pain is a sensation which, according to common but erroneous belief, is the 

 result of sufficiently intensifying any of the simple sensations. 



Pains have received various names to distinguish their quality, according to 

 the mode in which experience shows they may have been produced, as cutting,, 

 tearing, burning, grinding, etc. One peculiar mark that distinguishes painful 

 sensations is the lack of complete localization. While lesser pains are referred 

 with fair exactness to different parts of the body, and even to those internal 

 parts devoid of tactile sensibility, greater pains radiate and seem diffused over 

 neighboring parts. Pain also differs from special sensation in the long latent 



1 Goldscheider : Du Bois-Reymond 's Archiv fur Physiologic, 1886, 1887; Blix: Zeitschrift fur 

 Biologic, 1884; Donaldson : Mind, vol. 39, 1885. 



2 Czermak: Sitzungsberichte d. Wiener Akad., 1855, p. 500; Klug: Arb. d. physiol Anstalt zu. 

 Leipzig, 1876, p. 168. 



