210 



METABOLIC HORMONES 



the freshwater medium, and its action is facilitated by hormones 



of the ADRENAL CORTEX. 



Fig. 5-12. Increase in the apparent rates of active sodium-ion 

 uptake through the skin, produced by salt-depletion of (a) the 

 intact common frog and (b) the toad (after Jorgensen). (c) The 

 apparently similar effect of Pituitrin (a neurohypophysial extract) 

 on the isolated skin of the edible frog (from Fuhrman and Ussing, 

 in Sawyer, 1956). 



In the intact animal there is evidence for independent absorption 

 of both sodium and chloride ions against the osmotic gradient 

 (Jorgensen, Levi and Zerahn, 1954), from external concentrations 

 as low as 10~^ M.NaCl. Like the gills oiEriocheir^ even the isolated 

 frog's skin passes ions through itself from the outer surface to the 

 inner ("controls", Fig. 5-12 a-c) by active transport. This trans- 

 port is increased in intact frogs and toads after the tissues have 

 been depleted of salt by "washing" in distilled water for some 

 time (Fig. S-\2a and h). Since salt uptake is reduced in adrenal- 

 ectomized animals, it is assumed that hormones of the adrenal 

 cortex may stimulate the active transport of sodium ions inwards 

 through the skin, as they do through the kidney tubules (see 

 below). 



Despite the fact that the action of extracts of the adrenal cortex 



