in their Structure and Functiom, 391 



and scaly ; in the birch, it is soft and smooth. On the stem 

 of plants it is thick and tough ; but on the leaves, flowers, 

 and fruit, it is thin and delicate. The epidermis is continually 

 being renewed ; the old membrane falling off in small scales 

 as soon as the new one is formed. When destroyed by acci- 

 dent, it is regenerated with surprising celerity. Its use is to 

 defend from injury the parts over which it is spread, and to 

 prevent too speedy exhalation from the surface. The cellular 

 integument lies immediately under the epidermis or cuticle. 

 It is an extremely succulent substance, and is the part in 

 which the colour of vegetables resides. It is white, for in- 

 stance, in the stem of the birch, and green in that of the 

 apple tree. In most leaves it is green ; in some it is yellow, 

 and in some red or brown ; but it is in flowers that it displays 

 its most diversified and matchless hues. The true bark or 

 third tegumental layer of vegetables is situated beneath the 

 cellular integument. It is composed of innumerable vessels, 

 and after maceration it exhibits a reticulated structure. The 

 inner surface is softer and less dense than the outer one, and 

 is called the liber. Such are the characters of the external 

 covering of vegetables. How very closely they resemble 

 those belonging to the skin of animals will be seen in the 

 description which I shall now give of the latter substance. 



The cutaneous system of animals, like that of plants, is 

 composed of three separate laminae, which have received 

 appropriate appellations : the first, or outermost, is termed 

 the epidermis, or cuticle ; the second is denominated the rete 

 mucosum ; and the innermost is called the cutis, or true skin. 

 The epidermis is a thin semitransparent insensible substance, 

 of a very light grey colour ; readily separated fi:*om the sub- 

 jacent parts, by the application of boiling water and by blisters. 

 It not only covers the whole of the external surface of the 

 body, but is reflected into and lines the large passages ; as the 

 mouth, the alimentary canal, the trachea, &c. : so that it is 

 the most extensive membrane of the body, and is the only 

 organ, except the teeth, which comes in contact with the 

 atmospheric air. It allows free passage to the cutaneous per- 

 spiration and to the absorption of substances from without; 

 and yet anatomists have expressed themselves unable to prove 

 that it is perforated with pores. It exhibits different degrees 

 of thickness in different parts of the body. On the inner 

 edge of the eyelid, for example, it is very thin and diaphanous ; 

 while on the palms of the hands and the soles of the feet, 

 it is found, even in the fcetus, thick and of great density. 



In almost every species of animal it presents some peculiar 

 modification. In the human race it is sm(X)th and glossy j 



c c 4 



