6 PRACTICAL PHYSIOLOGY 



LESSON I 

 SENSATIONS CONNECTED WITH THE SKIN 



Sections of skin showing the epidermis, dermis, papillae, if possible 

 with .tactile corpuscles, and hair follicles, should be studied under 

 the microscopes. 



I. Sense of Contact Touch 



1. Is Contact felt equally all over the Surface ? 



METHOD. (1 ) Fit two or three brush bristles of different strengths 

 into split wooden matches. One student now lays his hand on the 

 table, palm downwards, and closes his eyes. The other touches 

 various points close together over a small part of the back of the 

 hand, about 1 cm. square, and the student experimented upon says 

 whether he feels the contact or not. The points on which contact 

 are most clearly felt are mapped out (Pressure Spots). 



(2) He now passes a small fragment of soft cotton wool lightly 

 over different areas of skin, and notes the sensation produced, and 

 whether all parts are equally sensitive. 



2. What Differences of Pressure can be distinguished? 



METHOD. One student lays his hand on the table, palm upwards. 

 He keeps his eyes closed while another student applies to the palmar 

 aspect of the proximal phalanx of the middle finger the different 

 weights supplied. The weights must be applied to the same place 

 in the same way each time, and at as nearly as possible equal inter- 

 vals of time. They must be left on for the same time, not more 

 than about 3 seconds. As each weight is applied the subject of the 

 experiment says "the same," unless he is sure that there is a 

 difference, in which case he says "heavier" or "lighter." 



Recording the result of each observation, the experimenter then 

 calculates and records the smallest percentage difference of weight 

 which can be appreciated with certainty. The weights used 

 are marked in units ; their absolute values, within limits, are 

 immaterial. 



3. Can Points of Contact be discriminated equally well at different Parts 

 of the Surface ? 



METHOD. This may be determined by finding how near to one 

 another two contacts may be made and felt as two and not simply 

 as one contact. 



One student closes his eyes and lays his hand, palm downwards, 

 on the table. The experimenter then takes a pair of compasses, 

 and, holding them loosely in the hand with the points somewhat 

 separated from one another, he lightly brings either one point or 

 the two points simultaneously down upon the back of the subject's 

 hand. The subject must say " one " unless he is certain that he 

 feels two points of contact. Working in this way, and recording 



