60 DERM IS AND EPIDERMIS. 



cise to which it is not accustomed, liquid collects between 

 the cuticle and the dermis, causing the blister. 



3. What we may Learn from a Blistered Hand. When 

 you open a blister, you feel no pain when cutting 

 through its outer covering; but if you touch the raw 

 surface beneath, it smarts. This shows that the epider- 

 mis has little or no feeling, while the dermis is very 

 sensitive. You may also obsefve that when you cut 

 through the cuticle, there is no bleeding; but if you 

 gently prick with a pin-point the dermis under the 

 blister, blood will flow. This shows that the dermis 

 contains blood and the epidermis does not. 



4. Other Illustrations of the Difference between the Der- 

 mis and Epidermis. Without waiting for a blister, you 

 may readily learn the facts described in the preceding 

 paragraph. Take a small needle threaded with fine silk, 

 and, if you are careful not to go deep, you can em- 

 broider a pattern on your hand without causing pain or 

 drawing blood. But if the point of the needle enters 

 the dermis, you feel the prick, and a drop of blood is 

 very likely to flow from the wound. 



5. How the Epidermis is Shed and Renewed. If you have 

 ever seen an old brick house, you may have noticed that the 

 bricks on the outside of the wall are worn away, crumbly, 

 easily broken, and the mortar between them loose; while 

 the bricks and mortar which lie deeper in the wall and 

 have not been exposed to the weather, are perfectly 

 sound. The epidermis (Fig. 21) is made up of millions 



3. How may we learn from a blister which layer of the skin is sen- 

 sitive ? How discover which contains blood ? 



4. How may we in another way observe the same facts ? 



5. What might you notice on an old brick house? How do its 

 walls resemble the epidermis ? Of what is the epidermis made up ? 



