300 EXPERIMENTAL PHYSIOLOGY. 



(6.) Press the ulnar nerve at the elbow, the prickling 

 feeling is referred to the skin on the ulnar side of the hand. 



5. Illusions. 



(a.) Place a thin disc of cold lead the size of a florin on 

 the forehead of a person whose eyes are closed, remove the 

 disc, and on the same spot place two warm discs of equal 

 size. The person will judge the latter to be about the same 

 weight, or lighter, than the single cold disc. 



(6.) Compare two similar wooden discs, and let the dia- 

 meter of one be slightly greater than that of the other. 

 Heat the smaller one over 50 C., and it will be judged 

 heavier than the larger cold one. 



(c.) Lay on different parts of the skin a small square 

 piece of paper with a small central hole in it. Let the 

 person close his eyes, while another person gently touches 

 the uncovered piece of skin with cotton wool, or brings 

 near it a hot body. In each case ask the observed person 

 to distinguish between them. He will always succeed on 

 the volar side of the hand, but occasionally fail on the 

 dorsal surface of the hand, the extensor surface of the arm, 

 and very frequently on the skin of the back. 



6. The Muscular Sense. 



(a.) With the arm and hand unsupported, the eyelids 

 closed, and the same precautions as in 3 (a.), determine 

 the smallest difference which can be perceived between two 

 weights. It will be less than in cartridges filled with a 

 known weight of shot, and tested by the pressure sense 

 alone. The cartridges, e.g., 100 grms., are numbered, but 

 they are so made as to have a small increasing increment of 

 weight. They are alike in external appearance. 



(6.) Take two equal iron or lead weights, heat one and 

 leave the other cold. The cold one will feel the heavier. 



7. Taste and Smell. Prepare a strong solution of sulphate of 

 quinine, with the aid of a little sulphuric acid to dissolve it 

 (bitter), a 5 per cent, solution of sugar (sweet), a 10 per cent. 



