948 CUTANEOUS SENSATIONS. 



organs of "warmth" than of "cold." Ruffini 1 describes, in the deeper layers 

 of the skin of the hand, end-organs of larger size, and cylindrical form, placed 

 more deeply than any other end-organs there. These organs of Ruffini have 

 been found also in the skin of the eyelid and of the upper arm, and therefore 

 appear of pretty general distribution, v. Frey suggests that they are the 

 organs of "warmth spots." 



Instruments employed for applying thermal stimuli to the skin are 

 usually called thermo-sestliesiometers. Many forms of them have been 

 employed. Drops of warm or cold fluid, 2 heated or cooled metal 

 pencils, 3 wires, 4 tiny plates of known surface and thickness, and made of 

 silver, 5 or other metal of known thermal capacity and conductivity, or 

 offering electrical resistance, have been employed. Kronecker intro- 

 duced a modification of his perfusion cannula for this purpose, and 

 Miescher-Ruysch further elaborated the same instrument. For many 

 observations the Kronecker-Miescher thermo-sesthesiometer is the most 

 handy and the best. 



It consists of a conical tube (German silver) 45 mm. long, divided 

 longitudinally by a partition, which is incomplete below at the apex of the 

 cone. The end of the cone is a circular platinum plate 1 mm. in diameter. 

 One compartment of the instrument is connected with an inlet, to which an 

 indiarubber tube can be attacbed. The other compartment is connected 

 in similar fashion with an outlet. Warmed or cooled water that is made to 

 flow through the instrument, can only pass from the inlet compartment into 

 the outlet compartment by the hole at the apex of the cone. The bulb of a fine 

 thermometer is placed in the compartment that leads to the outlet ; it is so 

 mounted that it is not affected by the warmth of the hand holding the 

 instrument. The whole instrument weighs 50 grms., and is held like a 

 drawing pencil. The water supplied to it should be filtered clear, and not 

 hard. Control experiments with the instrument have shown that the 

 temperature of the apex is, when water more than 26° C. above the tempera- 

 ture of the room flows through at 15 c.c. per minute, estimable within "1° C. 

 if *1* be subtracted from the reading of the thermometer at any moment. 

 When used at temperatures less different from that of the room, the correct- 

 ness is greater. 



Some observers 6 have used radiant heat for excitation. 



2. The degree of thermal sensitivity of different regions of 

 skin. — This is determined partly by the thickness of regional distri- 

 bution of the " cold spots " and " warmth spots," as described in the 

 preceding paragraphs, partly also by the sensifacient efficiency of the 

 individual thermal " spots," also in some respects by the relative thermal 

 conductivity of the skin, which is chiefly conditioned by the thickness 

 of its epidermis and its moisture. Only by testing with surfaces of not 

 much less than 100 mm. sq. can the grade of general sensibility of a 

 skin region be ascertained. 7 



Weber's estimations 8 were carried out by testing the degree to 

 which, at various regions of the body surface, distinction 9 can be made 



1 Atti d. r. Accad. d. Lincei CI. di sc. fis., mat. c nat., Roma, November 1893. 

 - Goldscheider, loc. cit. 3 Goldscheider, loc. cit. 



4 v. Frey, loc. cit.; F. Kiesow, Phil. Stud., Leipzig, 1898, Bd. xiv. S. 583. 



5 Sydney Alnitz, Skandin. Arch. f. Physiol., Leipzig, 1897, Bd. vii. 



6 Rauber, Centralbl. f. d. med. Wissensch., Berlin, 1869, S. 273; Tanzi, " Sulle 

 sensazioni del freddo e del caldo," Torino-Milano, 1886. 



7 Goldscheider, loc. cit. 8 Weber, loc. cit. 



9 Nothnagel's estimations of regional thermal sensitivity were made in the same way ; 

 so also Eulenbnrg's, Monatsh. f. pralct. Dermat., Hamburg u. Leipzig, 1885, Bd. iv., and 

 Ztschr. f. Min. Med. , Berlin, Bd. ix. 



