260 THE HUMAN SKIN : 



in the appearance of the strata of epidermis on vertical section, so 

 much so that the various layers have been described separately, 

 and are usually divided into four : — 



I.— Stratum Malpighi, 2.— Stratum Granulosum. 

 3. — Stratum Lucidum. 4. — Stratum Corneum. 



The constant friction of the body surface against external sur- 

 roundings causes the superficial layers to be constantly rubbed off, 

 and these are replaced by the next row below becoming the super- 

 ficial layer, and in turn being rubbed off; so that, in a short time, 

 the epidermis would be rubbed away altogether were it not that 

 new cells are constantly being formed in the lower portions of the 

 Stratum Malpighi, and push upwards the upper layers. The epider- 

 mis contains no blood-vessels. 



We now come to the lower, or true skin — the Dermis. You 

 are all aware, by painful experience, that the epidermis can be 

 removed during life, and expose below the true skin ; if not, the 

 experiment is a simple one : — Knock your knuckle against the 

 catch of the door or corner of the table, you will then see the 

 exposed dermis, in which the blood vessels are running, looking 

 red and bleeding slowly. It is exceedingly tender ; place the in- 

 jured finger in soapy water and prove this for yourselves ; for it 

 contains the nerve endings, or communications with the central 

 nervous system, which is, by their stimulation, informed of some- 

 thing wrong in the skin department; just as surely as the breakage 

 of crockery in the China department of our hypothetical Supply 

 Stores will reach the ears of the Directors, causing them pain and 

 annoyance, which will be the greater, the greater the damage. 



If we examine this dermis in vertical section under the micro- 

 scope, we find that it is a much looser material than the epidermis, 

 consisting of interlacing bundles of wavy fibres running in various 

 directions, with a few cells scattered here and there ; the whole 

 being something like a dense layer of straw. Running all through 

 this layer is a fine network of blood vessels, of very small size, and 

 the fulness or emptiness of these gives the redness or pallor to the 

 skin. Moreover, the whole thickness of the dermis is soaked or 

 saturated with a clear yellowish fluid, which has exuded from the 

 walls of the blood vessels, and is called lymph. This lymph 

 becomes very evident, in the little experiment of knocking the 



