ELEMENTARY EXPERIMENTAL PHYSIOLOGY 7 



the result of each observation as to the distance of the points and 

 the resulting sensation, the experimenter determines and records 

 how far the points must be apart on the back of the hand to give 

 rise with certainty to a double sensation. 



The observation is next to be repeated on the palmar aspect of 

 the terminal phalanx of the forefinger and on the dorsal aspect of 

 the forearm. 



4. Can Contacts be distinguished however rapidly they follow one 

 another ? 



METHOD. Place the ringer upon the toothed wheel, first when 

 it is rotating slowly and then when it is rotating rapidly, and note 

 in each case if a series of sensations or a continuous sensation is 

 experienced. The contacts are practically instantaneous. What 

 conclusions do you draw as to the duration of the sensations ? 



The Possibilities of Erroneous Interpretations of Tactile Sensa- 

 tions. (1) Aristotle's Experiment. Cross the middle finger over 

 the forefinger of the same hand and apply a pencil to the adjacent 

 surfaces. Note the character of the perception and the judgment 

 founded upon it. 



(2) Dip a finger into the glass of mercury and hold it there for 

 some minutes. Now notice where the sense of pressure is experi- 

 enced. It is at the surface of the mercury that the finger is subjected 

 to different degrees of pressure. 



What do you conclude to be the basis of our sense of pressure ? 

 Is it absolute pressure or differences of pressure at different parts of 

 the skin ? 



(3) One student lays his hand palm downwards on the table. 

 His companion now lets the weight provided come to rest first 

 suddenly and then very slowly on the back of his hand. Does the 

 weight feel equally heavy in both cases ? 



Is it the actual weight which is appreciated or the suddenness of 

 the change of weight in time ? 



II. Sense of Pain 



1. Can Pain be produced egually on Stimulating all Parts of the Skin ? 



METHOD. With a very fine needle explore the same small part of 

 the skin as in I. 1, p. 6, and map the result. Determine whether 

 the spots, the stimulation of which give rise to the most intense 

 sense of pain, correspond with those giving rise to the most marked 

 sense of touch. 



III. Sense of Temperature 

 1. Is the actual Temperature appreciated ? 



METHOD. Take three basins. 1. Fill one with water so warm 

 that the hand can be just comfortably held in it. 2. Fill another 

 with cold water. 3. Fill the third with water at a temperature 

 intermediate between 1 and 2. 



Place one hand in 1 and the other in 2, and after keeping them 



