70 PERSONAL APPEARANCES IN HEALTH AND DISEASE. 



The skin, which serves as the protective covering 

 of the body, is a tough membranous structure, con- 

 sisting of three parts, an external layer of epidermis or 

 scarf-skin, an internal, sensitive and vascular layer called 

 cerium or true skin, and an intervening soft, spongy layer 

 called the rete mucosum^ or, after its discoverer, rete 

 Malpighii. This middle layer is the seat of collections 

 of fine pigment granules, which are the primary cause of 

 diversity of colour. In dark persons this layer is thicker, 

 more spongy, and contains more pigment than in fair 

 ones, whilst in the Ethiopians it is very thick and very 

 black, so that the colour of the blood in the underlying 

 corium is never seen at all. There are some diseases, 

 one especially, and that of rare occurrence, which are 

 marked by a gradually increasing deposit of this pigment, 

 so that a previously fair skin may become gradually more 

 and more bronzed,* the regions which are naturally the 

 seat of most pigment being those which suffer most. 



A "bruise" is the name given to the effect . produced 

 on the skin by an injury which does not suffice to break 

 the skin but only to contuse it. The blood escaping 

 from such blood-vessels as are torn in the injury ^ collects 

 under the skin, and the gradual variation in tint that a 



* So marked is this that the affection in question has been styled 

 " Bronzed-skin Disease," although the coloration of the skin is only 

 a part, and that a small part, of a deep-seated disorder. 



