AND PHYSIOLOGY. 



295 



no longer of service to the body. Certain it is that no other 

 organ in the body has as yet been discovered which subserves 

 this purpose, and equally certain that in cases, where large 

 wounds are to be healed, and in certain other conditions of 

 the body, the white corpuscles are greatly increased in num- 

 ber. 



518. The Skin. — Among those organs whose offices are 

 those of absorption and secretion, the Skin finds a prominent 

 place. 



519. Made up of Three Membranes. — This is a membrane 

 simple in its general aspect, but under the microscope it is 

 found to be composed of no less than three distinct layers : 

 the Epidermis, Basement Membrane, and Cerium. It covers 

 every part of the body, except the portion immediately sur- 

 rounding the various orifices, and those portions of the ex- 

 tremities covered by the nails. It is highly elastic, as may 

 be seen by the gaping of a long gash, and possesses a certain 

 amount of contractility, owing to some muscular fibers con- 

 tained in it. 



520. Pa pill ED ; their Size. — Upon several portions of the 

 body the skin is roughened by small protuberances, either 

 arranged in a circular form, or in rows, which are supplied 

 with one or more loops of 



nerves. These are termed Fig. 286. 



Papillae, and are found most 

 abundantly in the extremi- 

 ties, and especially upon the 

 palms of the hand and soles 

 of the foot. They vary in 

 height from ~Vrd to -?\d of a 



° _ °" Papillfe from Palm of the Hand, magm- 



line, being of different lengths fied thirty-five times, 

 in different parts of the body. 



519. Of what three membranes is the skin made up? State their sreneral proper- 

 ties. 520. What are the papillae? Where are they found in the greatest numbers? 

 State their size. 



13* 



