10 



ELEMENTS OF PHYSIOLOGY 



The skin covering the base of that the nail is renewed in 



the nail is cut back. 



four months. 



near their roots, are alive and receive nourishment. The 

 root of the nail is in a kind of groove or fold of the true 

 skin (Fig. 9) at the bottom of which papillae are very 

 numerous. The nail may be regarded as a very wide, flat 

 hair. The nail grows not only at its 

 root, but along its bed which is of true 

 skin (Fig. 10). Hence, its thickness 

 increases as it approaches the tip. If 

 the epidermis is pressed back at the 

 root, the nail may not be perfectly 

 nourished, and a white speck or flaw 

 is formed, which travels slowly along 

 FIG. 9. End of Finger, with the growth of the nail. It is said 



three or 



If you note the date of 

 the appearance of a scar at the base of the nail and note 

 when it has traveled to the tip, you can find whether this is 

 true. Find whether or not a nail is transparent, by looking 

 through the tip of the nail, held up to the light. The 

 nails stiffen the ends of the fingers 

 and aid in handling small objects. 

 Can you pick up a pin without 

 using the nails ? Corresponding 

 organs in the lower animals are 

 claws and hoofs. The epidermis 

 forms also the scales, feathers, and 

 horns of the lower animals. 



13. The papillae over a small 

 area, when the epidermis is weak, 



sometimes become overgrown, so that they project above 

 the skin, and form a wart. If it is burned away with 

 acid, the epidermis will grow over the place. Why is a 

 wart rough ? How does it differ from a mole ? Which 

 is more likely to increase in size ? Which has more pig- 

 ment ? Which contains hairs ? When the epidermis is 



FIG. io. Section of Nail and 

 Parts Beneath. 



I, 2, 4, horny layer of cuticle, con- 

 tinuous with 3, the nail; 9, 12, 

 dermis. 



