230 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



Certainly the outermost layers, which become cornified, must be considered as 

 being composed of cells of low metabolism. The structures which one would 

 suspect mostly as those involved in active transport are the epithelial cells of 

 the stratum germinativum which are lined up in only one or two rows. 

 A few preliminary measurements on skin of Rana pipiens have given the 



Fig. i6. Eleclronmicroscopic view of frog skin. Arrow points to the 'Basement membrane'. 

 Rana teinporaria (56). (Reproduced from original prints by courtesy of Prof. Dr. F. S. Sjoe- 

 strand, Stockholm.) 



following information: i gm of skin represents, on an average, an area of about 

 45 cm-. The thickness of the total fresh skin lies between o.i and 0.25 mm. Plani- 

 metric measurements showed that, in the average cross section of fixed skin of 

 the leg, the area occupied by all the epithelial cells of the epidermis represents 

 about one fourth of the total cross-sectional area of the skin. For the area of 

 epithelial cells of the stratum germinativum, this figure is of the order of one 

 eleventh. Similarly approximate values were obtained for the epithelium of the 



