542 ELEMENTARY PHYSIOLOGY less. 



body has been more or less extensively converted into 

 horny substance. 



Thus the cast-off epidermis in reality consists of more 

 or less coherent masses of cornified nucleated cells. 



There is a yet simpler method of demonstrating this 

 truth. At the margins of the lips the epidermis is 

 continued into the interior of the mouth, and though it 

 now receives the name of epithelium it differs from the 

 rest of the skin in no essential respect except that it is 

 very thin, and allows the blood in the vessels of the 

 subjacent dermis to shine through. Let the lower lip be 

 tu»"ned down, its surface veiy gently scraped with a blunt- 



Pio. 175. — Two Epithelial Scales from the Interior of the Mouth. 



A small nucleus n is seen in euoh, a.s well as fine granulations in the 

 body of the plate. The edges of the plates are irregular from pressure. 

 Magnified about 400 times. 



edged knife, and the substance removed be spread out, 

 and covered with a thin glass, and examined as before. 

 The whole field of view will then be seen to be spread 

 over with flat irregular bodies very like the epidermic 

 scales, but more transparent, and each provided with a 

 nucleus in its centre (Fig. 175). 



Since these detached scales are always to be found 

 on the inner surface of the lip, it follows that they are 

 always being thrown off. 



7. The Growth of the Epidermis. — The homy 

 external layer of the epidermis is composed of coherent 



