THE SENSES 



977 



pass inwards, each line of hair-bulbs requiring a heavier pressure 

 than the line external to it, till at last 3! or 4 grammes' pressure 

 is needed to cause a sensation of touch, and inside of this line of 

 hairs the skin does not respond at all. When a bristle of this 

 pressure fails to elicit touch sensation, no greater pressure will in 

 general do so (Fig. 429). 



For thermal sensibility there is also a region of complete 



FIG. 429. MIDDLE CUTANEOUS : LEFT THIGH (TROTTER AND DAVIES) 

 (REDUCED BY ONE-THIRD LINEAR). 



Twenty-six days after section. Results of examination with v. Frey hairs. 

 Touch spots marked responded to hair of 280 milligrammes' pressure ; those 

 marked o to hair of 800 milligrammes ; and those marked + to hair of 2,280 milli- 

 grammes. The continuous line marks the limit within which there was anaesthesia 

 to the camel's-hair brush. 



anaesthesia and a region of partial anaesthesia. The best way of 

 outlining these is the use of a temperature of o C. as the stimulus 

 (Fig. 430). 



Outside the zone of complete thermal anaesthesia there is a 

 region in which temperature sensations are distinctly elicited, 

 but do not possess the normal intensity, the temperature of 



62 



