STUDY OF THE SKIN. 81 



2. Run the point of a clean needle beneath the 



thin outer layer of the skin on the palm 

 of the hand. 



a. Does the needle cause blood to flow? 



Is the outer layer of skin (epider- 

 mis) supplied with blood-vessels? 



b. Does the insertion of the needle cause 



any pain? Can you feel the point 

 of the needle touch the skin? 

 Would you infer that nerves en- 

 tered the epidermis or not? 



3. In what regions of the surface of the hand 



is the epidermis thickest? How do you 

 know? In what region is it thinnest? 



4. Press the tip of the forefinger on a piece of 



cloth covered with some thick ink (prin- 

 ter's ink or mimeograph ink is best), then 

 press the finger-tip on a page in your note 

 book. Study the impression made. 



a. Are the black lines (made by the 



ridges on the finger) all of the same 

 width? Are they all parallel to 

 one another? 



b. In the same way take the impression 



of the tips of your other fingers and 

 of your thumb. In what respects 

 do these various impressions 

 differ? 



c. Where else on your hand can you see 



similar ridges? 



d. What other lines are visible on the 



palm of the hand? 



