LAW OF PERIPHERAL PROJECTION. 299 



(c.) Plunge the hand into water at 36 C. One experiences 

 a feeling of heat. Then plunge it into water at 30 C., at 

 first it feels cold, because heat is abstracted from the hand. 

 Plunge the other hand direct into water at 30 C. without 

 previously placing it in water at 36 C., it will feel pleasantly 

 warm. 



(d.) Hold one hand for a time in water at 10 C., and 

 afterwards place it in water at 20 C., at first the latter 

 causes a sensation of heat, which soon gives place to that of 

 cold. 



(e.) Test with the finger the acuteness of the sense of 

 temperature i.e., in two given fluids of different temper- 

 atures, what fraction of a degree C. can be distinguished. 

 One can usually distinguish |-, although the acuteness is 

 greater when the fluids are about 30 C. 



(/.) Use two brass tubes (5 cm. long and 1 cm. in diam.), 

 terminating in a point. Cover both, all except the point, 

 with india-rubber tubing. Fill one with warm water and 

 the other with cold. Test the position of the warm and 

 cold points on another person on various parts of the skin. 



3. The Sense of Pressure. 



(a.) Rest the dorsum of the hand on a table, cover a small 

 area of the palm with a non-conducting material e.g., a 

 wooden disc or vulcanite plate and on the latter place dif- 

 ferent weights, and estimate the smallest difference of weight 

 which can be appreciated. 



(b.) Dip the hand into* water of the same temperature as 

 the hand, or a finger into mercury. The greatest sensation 

 is felt at the plane of the fluid in the form of a ring, but 

 even this is best felt on moving the hand up and down. 



4. Law of Peripheral Projection. 



(a.) Dip the elbow in ice-cold water; at first one feels the 

 sensation of cold, owing to the effect on the cutaneous nerve- 

 endings. Afterwards, when the trunk of the ulnar nerve is 

 affected, the pain is felt in the skin of the ulnar side of the 

 hand where the nerve terminates. 



