ERNST G. HUF 



229 



^ = 



(|)S 



Gt-<pt - (Ga+ - G-)(RT/F)ln(a2/ai) 

 G+ + G- 



,H ^ G+-G-[(,p+ - 2(RT/F)ln(a2/ai)] 

 F(G+ + G-) 



The symbols have the following meanings: tp — spontaneous skin potential; 

 (pt = EMF of the sodium pump; G^ and G"~ = conductance in skin of the ac- 

 tively and passively transported ion; $ = net rate of salt uptake; others have 

 the conventional thermodynamic significance. 



If in active salt transport G~, rather than G^, is the dominant variable, it 

 can be shown that the correlation between skin potential and net active trans- 

 port of XaCl must be a negative one (28, 46). Since this is the case in normal 



* ^-^ ' 



-J 



Fig. 15. Cross section of frog 

 skin of the inner thigh. Rana 

 pipiens. 



skin, it has been concluded that, although sodium is the leading partner in 

 active salt transport, chloride ions determine largely the transport rate (28). 

 A positive correlation between net salt transport and skin potential should be 

 expected, if Ga is the dominating variable. 



MICROSCOPIC .AXD SUBMICROSCOPIC STRUCTURE OF FROG SKIN 



At various places in this discussion, it has become obvious that a detailed 

 knowledge of the microscopic and submicroscopic structure of the skin is essen- 

 tial in order to arrive at some idea as to which structural elements are possibly 

 involved in ion and water transport in surviving frog skin. The histology of 

 frog skin, using conventional techniques of preservation, sectioning and stain- 

 ing, is well known, of course. Figure 15 shows the essential histological elements 

 of skin. One sees a relatively large portion of the section occupied by cutis and 

 subcutis in which larger and smaller glands are embedded. Certain areas of the 

 skin carry a dark pigment. The epidermis of the skin consists of various layers 

 of epithelial cells, not all of them, one would presume, having the same vitality. 



