232 



METABOLIC HORMONES 



Xenopus, the wholly aquatic clawed toad, shows little increase 

 in water uptake in response to ADH injection; but the terres- 

 trial toad, Bufo americana, (though not Bufo bufo; Saw}^er, 1956) 

 shows a greater increase than the frog. Moreover, the toad is able 



100 200 300 400 



Milliosmols NaCl / Jitre, in bath 



Fig. 5-22. Percentage change in weight of the frog, Rana, after 

 immersion for 3 hr each time, in baths of different osmotic 

 concentration. Increase and decrease in weight, due to change in 

 water content, are shown as ordinates above and below the hori- 

 zontal line; values for osmotic concentration as abscissae range 

 from distilled water, O, to values above that of plasma {ca. 325 

 milliosmols). Control frogs maintain a constant value over much 

 of this range; but frogs that had received 5 units/ 100 g body- 

 weight of NEUROHYPOPHYSIAL EXTRACT (frog ADH) allow a free 

 flow of water through their skin, so that their weight changes 

 steadily until they come each time into osmotic equilibrium with 

 the external medium (from Sawyer, 1951). 



to take up water from damp moss and does not need to be sub- 

 merged like the frog. There therefore seems to be an adaptive 

 correlation between the sensitivity of the skin to the hormone and 

 the degree of adaptation to land life. The neurosecretory material 

 in the neurohypophysis is found to be depleted in dehydrated 

 frogs, indicating that it has been secreted in response to the need 

 to absorb water. 



