102 ELEMENTARY PIIYSIOLOGYo XX. 



similarly line after line of the square. It will be found 

 that in some places cold is felt keenly and at once, in 

 other places dully, and in others not at all. 



Test the cold spots again, and mark the points most 

 sensitive to cold with methylene blue. In re-testing, an 

 interval of a few seconds must be allowed between two 

 applications to the same spot. 



3. Sensation of heat in different parts of the 

 skin. Dip a small metallic knob (or a bulb of a mercury 

 thermometer) into water at 65 C. to 70 C., quickly dry 

 it, and apply it to the fore-arm, and note the sensation. 

 Warm it again, and apply it to the forehead, the sensa- 

 tion of heat will probably be much greater than in the 

 preceding case. Compare similarly, the tip of the finger, 

 the cheek, and the palm of the hand and the back of the 

 neck. 



4. Warm spots in the skin. Proceed as in 2, but 

 warm the rods in water to 55 C., or as hot as can be 

 borne without pain, and mark out the spots where heat 

 is felt. The results will probably be much less precise 

 than in the case of the cold spots. 



5. Touch lightly with a piece of cotton wool the tip 

 of the forefinger, the skin below the nail, and the hairs on 

 the wrist. Note the difference in the delicacy of sensa- 

 tion. 



6. Successive temperature contrast. Put one hand 

 into water of 40 C. and the other into ice-cold water. 

 After a minute put both into water of 20 C. This water 

 will feel warm to the hand which has been in the cold 

 water and cold to the hand which has been in the hot 

 water. 



