THE KIDNEYS AND SKIN. 441 



such influence is mainly due to vaso-motor changes either 

 paralysis of the renal vaso-constrictor nerves or stimulation 

 of the vaso-dilator. Such changes would account for the 

 phenomenon, and there is no evidence of the existence of 

 true secretory nerves acting directly on the cells of the 

 organ as certain fibres of the chorda tympani (Chap. XIX) 

 do on the cells of the submaxillary gland. 



The Skin, which covers the whole exterior of the Body, 

 consists everywhere of two distinct layers ; an outer, the cuti- 

 cle or epidermis, and a deeper, the dermis, cutis vera, or 

 corium. A blister is due to the accumulation of liquid be- 

 tween these two layers. The hairs and nails are excessively 

 developed parts of the epidermis. 



The Epidermis, Fig. 135, consists of cells, arranged in 

 many layers, and united by a small amount of cementing 

 substance. The deepest layer, d, is composed of elongated 

 or columnar cells, set on with their long axes perpendicular 

 to the corium beneath. To it succeed several layers of round- 

 ish cells, b, the deepest of which, prickle cells, are covered by 

 minute processes (not indicated in the figure) which do not 

 interlock but join end to end so as to leave narrow spaces 

 between the cells ; in more external layers the cells become 

 more and more flattened in a plane parallel to the surface. 

 The outermost epidermic stratum is composed of many layers 

 of extremely flattened cells from which the nuclei (conspicu- 

 ous in the deeper layers) have disappeared. These super- 

 ficial cells are dead and are constantly being shed from the 

 surface of the Body, while their place is taken by new cells, 

 formed in the deeper layers, and pushed up to the surface 

 and flattened in their progress. The change in the form of 

 the cells as they travel outwards is accompanied by chemical 

 changes, and they finally constitute a semitransparent dry 

 horny stratum, a, distinct from the deeper, more opaque and 

 softer Mfilpiffhiftn or mucous layer, b and d, of the epider- 

 mis. The cells of this latter, in spite of their name, are not 

 muceginous; they are soluble in acetic acid; those of the 

 horny stratum not. 



The rolls of material which are peeled off the skin in the 

 "shampooing^ of the Turkish bath, or by rubbing with a 

 rough towel after an ordinary warm bath, are the dead outer 

 scales of the horny stratum of the epidermis. 



