

SENSATIONS OF TEMPERATURE 459 



The presence of different temperature points has been established not only 

 by use of the appropriate temperature stimuli but also by mechanical, electrical 

 and chemical stimulation. 



The sensation which is produced by stimulation of a single temperature 

 point is not "pointlike"; instead, one experiences a sort of irradiation of 

 the feeling, so that the sensation is more extensive than the temperature point 

 i. e., it appears to be disklike and at the same time to have depth. It is 

 on this account that the temperature sensations aroused by contact with warm 

 and cold objects appear to be perfectly continuous, giving no indication of 

 the pointlike arrangement of the end organs. Then we are inclined also to 

 fill up unconsciously all the gaps in our special sensations (cf. the blind spot 

 in the eye, Chapter XXI). 



The number of cold spots in the skin of an adult is found to be 6-23 per 

 square centimeter of surface ; the number of warm spots 0-3. The entire surface 

 of the body would contain, therefore, about 250,000 cold spots, and about 30,000 

 warm spots. In a child the temperature points appear to 

 stand closer together, and this may be taken to mean that 

 the child is born with his complete equipment of such 

 points. 



In order to obtain a more accurate idea of the topogra- 9 



phy of the temperature senses, Goldscheider has stimulated IS**** 

 different portions of the skin with the ends of cold and 

 hot rods 34 cm. in diameter. One cannot obtain the 

 number of temperature points by this method, but can FIG. 182. The arrange- 

 test the relative sensitivity of different regions very well. ent x of i cold S P* S 

 Thus if there be no temperature points in a certain por- 

 tion, application of the rods will produce no sensation of spots' (black)^ on 

 temperature at all ; if points are present, they may vary small area of the dor- 

 both in number and excitability, so that the degree of sal side of the left 

 sensitivity will vary. A surface with only a few intense wrist, after BUx. 

 points would give a stronger sensation than another with 



many weak points, etc. Fig. 183 is given as an example of the topographical 

 distribution of the cold and heat senses. 



Goldscheider summarizes his numerous experiments on this subject as 

 follows: (1) The cold sense is everywhere more perfectly developed both 

 extensively and intensively than the heat sense. (2) This relationship holds 

 as well for the parts of the skin habitually clothed as for the parts habitually 

 naked. Goldscheider finds the cause of this regional difference in the varying 

 number of nerve fibers supplied to the different places. Of course there should 

 be added also the varying thickness of the epidermis covering the end organs. 



The experiments of different authors agree fairly well with regard to the 

 acuteness of the temperature senses in the different regions. Those most sen- 

 sitive to temperature stimuli are the nipples, and the breast in general, the ala3 

 nasa?, the anterior parts of the arm ; then follow the outer angle of the eye, the 

 upper lip, the abdomen, the volar side of the forearm, the inner parts of the 

 thigh, the foreleg, etc. Least sensitive of all is the scalp. 



The hand is but slightly sensitive to temperature and in general it can be 

 said that those regions of the skin which are used especially for touch are less 

 sensitive to temperature than other regions. 



