- G Degani: MIGAL, Galilee Technological Centre, Kiryat Shimona, 10200, Israel.
1. The tolerance and adaptation to urea solutions by terrestrial green toads (Bufo viridis) and semi-aquatic frogs (Rana Ridibunda) were studied. 2. the green toad showed tolerance to urea solution of 800 mM and the frogs showed tolerance only to about 400 mM urea solution. 3. The plasma concentrations of both species was hyperosmotic to the external medium in all the different urea solutions. 4. Blood osmolality, urea, Na+ and Cl- concentrations of B. viridis were always higher than in R. ridibunda. 5. The urea concentration in muscle of R. ridibunda was higher than the urea concentration in muscle of B. viridis. 6. The muscle tissue weight loss of B. viridis was significantly lower than R. ridibunda.