FIVE FIGURES
The frog, like most other amphibians, is able to migrate from water to dry land and vice versa. I n doing this, changes occur in its water balance. When the frog is in water it will gain water by diffusion through the skin. The rate of uptake varies with the temperature and is 4-5 times as rapid at 30Β°C. as a t 0Β°C. (Overton, '04; Hevesy, Hofer and Krogh, '35). T h e n the frog is out of water, water evaporates freely from the surface of the skin at a high rate; and Overton found that a 60gm frog loses one-quarter of its weight in 8-11 hours a t ordinary room temperature and humidity (quoted from Krogh, '39).
The frog responds physiologically to changes in its cnvironment in such a way that it tcnds to maintain the water content of the body. TVhen the frog is in water the kidneys usually eliminate water at the same rate with which it is taken up. The rate of urine production therefore varies with the temperature. When out of water the urine flow decreases.
The purpose of the present study has been to investigate the changes in renal plasma flow, glomerular filtration rate and tubular reabsorption of water that are responsible for the changes in urine flow when the frog is exposed to changes in its environment.