PRACTICAL EXERCISES 1001 



placed on the skin at the same time, and the same pressure applied 

 to both. The subject must not see the points. 



(5) Time Discrimination of Touch. Touch the prong of a 

 vibrating tuning-fork lightly with the tip of the finger. The taps 

 of the prong on the skin do not blend into a continuous sensation 

 even when the fork vibrates several hundred times per second. 



30. Temperature Sensations. For the investigation of these, 

 pieces of thick copper wire, filed at one end to a blunt point, and 

 fixed by the other in a small wooden handle, may be used. They 

 can be heated in a sand-bath or in a beaker of water to the desired 

 temperature, or cooled in cold water or in ice. Or a metal tube 

 drawn out at one end, through which water at the required tem- 

 perature can be passed before use, may be employed. Another 

 device is a metal cylinder ending in a point, and filled with water 

 at the given temperature. 



(1) On the dorsal side of the hand outline an area of skin with a 

 pen or a coloured pencil. Divide this into areas of 4 square milli- 

 metres. Go over the area with a wire or cylinder at a temperature 

 of about 40 C., and determine the extent and position of the spots 

 which on contact yield a sensation of warmth, marking them on the 

 skin by ink-dots, or mapping them on ruled paper. Then repeat 

 the exploration with points at a temperature of about 15 C., and 

 map the spots which yield a sensation of coolness. Now note 

 whether a warm spot touched with a point at 15 C., or a cold spot 

 touched with a point at 40 C., yields any temperature sensation. 



(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 tempera- 

 ture 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 w r hich 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 ringer 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 



