298 SOLID PARTS OF ANIMALS. 



CHAPTER XIV. 



OF THE EPIDERMIS. 



THE epidermis or cuticle is the outer layer of the skin. Though 

 very thin in most parts, it becomes thick and indurated in the 

 soles of the feet, or wherever it is habitually subjected to pres- 

 ture. Its inner surface is smooth and uniform, being connect- 

 ed with the rete mucosum and corium by delicate filaments. But 

 it can be readily separated from them by decoction or macera- 

 sion in water. The outer surface presents in some places a num- 

 ber of waving excentric lines, which make it appear, when ex- 

 amined with a glass, ragged and uneven. It does not appear to 

 be composed of scales, as some anatomists have supposed ; but 

 rather to be a homogeneous membrane destitute of vessels and 

 nerves, and deposited on the skin as an insensible investment. 

 It is slightly elastic, and is easily ruptured. It wears away pretty 

 rapidly from all exposed parts, but is soon reproduced, and gra- 

 dually acquires its original thickness. 



If we heat a portion of the cuticle in the flame of a candle 

 it melts without bending or swelling up, then catches fire, and 

 burns with a clear flame, giving out the usual smell of burning 

 animal matter. It imbibes water with facility. When the cu- 

 ticle of the palm of the hand is kept long in water, it swells up, 

 becomes wrinkled, opaque, and white. When left long in wa- 

 ter, it becomes brittle without putrefying ; but how long soever 

 we boil it in water it does not dissolve in that liquid. 



If we let fall a drop of binoxide of hydrogen on any part of 

 the epidermis, it gives it a white colour, which disappears in a 

 few hours. The cuticle is insoluble in alcohol and ether, but 

 these liquids dissolve a small quantity of fatty matter, which the 

 epidermis in its natural state contains. Concentrated sulphuric 

 acid softens and gradually dissolves the cuticle. If we remove 

 the acid before it has dissolved the epidermis completely, it leaves 

 a dark brown spot. The part thus affected gradually becomes 

 hard and a new epidermis forms below it. When a piece of epi- 

 dermis is plunged into sulphuric acid, it becomes transparent 

 before it dissolves. Nitric acid softens it, and if we saturate the 

 excess of acid with ammonia, the stain acquires an orange colour. 



