KIDNEYS, SKIN, AND GENERAL EXCRETION. 



397 



divide, and thus the top layers of the epidermis are being 

 continually pushed further and further out by the addition 



Fig. 132. SECTION OF SKIN AJO> SUBCUTANEOUS TISSUE. (After Kolliker.) 

 a, horny layer; b, Malpighian layer of epidermis; c, corium; rf, subcutaneous fatty 

 tissue; e, papillae; f, fat; g, sweat gland; h, duct; i, mouth of sweat gland. 



of new cells from beneath. The layers of these derived 

 cells, lying close to the Malpighian layer, also resemble 

 the Malpighian layer in having well-defined nuclei and 

 in their cuboidal shape. But further outward a chem- 

 ical change sets in, by means of which the substance 

 of these cells seems changed into a horny material akin 

 to the keratin of ordinary horns, while in addition to 

 this chemical change they become more and more flattened, 

 losing more and more the appearance of cells until at the 

 top of the epidermis they occur as mere horny scales, which 

 from time to time, by contact with other bodies or by the 

 friction of towel, etc., are broken off from the skin. 



The layer of the epidermis in which this chemical change 

 takes place is readily visible in sections as much clearer 

 looking, due to the fact that the cells have undergone a 

 transformation into the somewhat transparent horny ma- 



