i "6 THE SENSES 



(2) Touch the skin with a test-tube containing water at 50 C. ( and 

 again with a test-tube containing ice. Do the sensations differ in any 

 way from those of pure warmth and coolness ? Repeat (i) with 

 temperatures of 50 and o, and note whether there is any difference 

 in the quality of the sensations yielded by the warm and cold spots. 

 When a cold spot is touched with a point at a temperature of 50, or 

 a warm spot with a point at a temperature of o, is any sensation 

 obtained ? If so, what ? 



(3) Apply successively to one and the same portion of the skin test- 

 tubes containing water at 50, 45, 40, 35, 30, 25, 20, 15, 10, 

 5, and o (ice), and determine the sensations excited in each case. 

 The contact should only be momentary, so as not to cause extensive 

 and lasting change of temperature of the skin. Note that there is a 

 certain range of temperature above and below that of the skin within 

 which no sensation of heat or cold is given. 



(4) Take three beakers of water at 20, 30, and 40 C. respectively. 

 Place a finger of one hand in the coldest beaker, a finger of the other 

 hand in the warmest, until no definite temperature sensations are felt 

 by either finger. Plunge both fingers into the beaker at 30 C. ( and 

 temperature sensations will be perceived. 



(5) Temperature Discrimination. Find the least perceptible differ- 

 ence in temperature between two beakers of water at about o C. 

 Repeat the experiment with two beakers of water at about 30 C., and 

 again with two beakers of water at about 55 C. Use the same hand. 

 Expose the same amount of surface to the water. 



(6) Compare the acuteness of the temperature sensations of the 

 skin and the mucous membrane of the mouth, touching a given portion 

 of skin and then a portion of mucous membrane with tubes containing 

 water at various temperatures. 



31. Pain. (i) Using a pin, explore a cutaneous area to determine 

 whether every point of the skin yields the painful sensation of pricking. 

 Especially compare the result of stimulating the region in the imme- 

 diate neighbourhood of the hairs with the spaces between hairs. Dis- 

 criminate the touch sensation given by the light contact of the pin-point 

 from the painful impression caused when the pressure is increased. 

 Note that the touch element is more evanescent than the pain element. 



(2) With strong v. Frey hairs determine the pressure at which the 

 sensation of touch passes into that of pain. 



(3) Compare the sensibility to pin-pricks of the mucous membrane 

 within the mouth with that of the skin. 



32. Having determined the systolic blood-pressure in one arm of 

 a fellow-student (p. 113), release the pressure in the cuff, then raise 

 the hand in the air so as to empty the arm of blood, and while it 

 is still raised, get up a pressure in the cuff equal to the systolic pressure. 

 Lower the hand and maintain this pressure by squeezing the bulb occa- 

 sionally. Be careful not to increase the pressure above the systolic 

 pressure. There is no disadvantage in letting it drop 5 to 10 milli- 

 metres below systolic pressure from time to time. Now compare the 

 acuity of the sensations of contact, pressure, warmth, cold, and pain 

 in the anaemic and the normal hand, always on symmetrically placed 

 areas of the two hands. Repeat the comparison at intervals till a 

 definite difference is found, and note the sensation for which the acuity 

 first diminishes. Do not prolong the experiment unduly. If the sub- 

 ject experiences discomfort, the pressure in the armlet is to be at once 

 released. 



