170 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



forehead or on the palm of the hand for about half a minute. Does the 

 sensation of cold continue even after the coin has been removed, allow- 

 ing the temperature of the skin to rise? Repeat this test with a slightly 

 heated coin. 



14. Acuity of the Temperature Sense. Insert the index-finger in a 

 beaker filled with water of 30 C. Raise the temperature of the water 

 quickly a few tenths of a degree. How small a difference are you able 

 to perceive? 



15. Temperature Contrast. Place the index-finger of your right 

 hand in water of 40 C. and the index-finger of your left hand in water of 

 20 C. Wait a short time until the initial sensations of warmth and 

 cold have become less intense. Transfer both fingers into water of 

 30 C. Note that the right finger feels cold because heat is lost by it, 

 whereas the left finger feels warm owing to a certain stagnation of its 

 heat. 



Place one index-finger hi water of 32 C. and the other in water of 

 45 C. Wait half a minute and transfer both in water of 10 C. An- 

 alyze the sensation. 



16. Thermal Illusions. Employ two disks of metal of equal size, 

 one warm and the other cold. Place them successively upon the skin 

 of the subject, whose eyes are closed. The cold disk will feel heavier 

 than the warm one. 



17. Pain Spots. Map out the dorsal surface of the hand of the sub- 

 ject with the point of a sewing needle, noting the points where a distinct 

 sensation of pain is perceived. 



18. Discrimination of Weight: Weber's Law, Place a small box 

 containing 10 shot upon the palmar surfaces of the tips of the middle 

 and index-fingers of the subject. Support his hand at the wrist, and 

 ask him to close his eyes. When he has obtained a clear impression of 

 the weight, add or subtract shot until he notices a distinct difference. 

 Repeat this experiment several times and obtain a mean value for the 

 number of shot added or removed. Repeat this test with 30 and 50 

 shot respectively in the box. Tabulate the results. 



19. Relation of Weight to Area Stimulated. Place two objects of 

 equal weight but unequal size upon the dorsal aspect of the subject's 

 hand, his eyes being closed. Most generally, that weight will be 

 thought to be heavier which presents a greater surface to the skin, 

 i. e., stimulates the largest number of tactile corpuscles. 



Request the subject to lift three cylinders of equal weight, but 

 unequal size, and determine which is the heaviest. The largest cylinder 

 is usually thought to be the heaviest. 



20. Illusions Relating to Weight. Lift an object first rapidly and 

 then slowly, and note that its weight seems less in the former instance. 

 Lift a certain weight with one hand while clenching the other. The 

 weight seems lighter in consequence of the simultaneous effort. 



21. Simultaneous Movements. Stand erect before a blackboard. 

 Close your eyes and draw with both hands placed at the same height two 



