Hormones and Homeostatic Mechanisms 179 



This is probably conditioned by the presence of a regulating 

 mechanism which after previous loading with water increases 

 the reabsorption of sodium. At the end of the preweaning 

 period there is a considerable change in the effect of cortisone 

 and cortexone on elimination of water and sodium after a 

 water load. Even 33-day-old animals, however, do not react 

 quantitatively in the same way as adult animals. This is 

 evidently due to the fact that only after the 33rd day does the 

 male adrenal begin to differ from that of the female. It may 

 be assumed from the results presented here that the reactivity 

 of the adrenals changes at the time of weaning. That change 

 can be in relation to the change in homeostatic mechanisms 

 regulating the intake of water and sodium which occurs at the 

 time of weaning. 



REFERENCES 



Capek, K., Hahn, p., Krecek, J., and Martinek, J. (1956). Studies 



on the Physiology of Young Mammals. Czechoslovak Academy 



Publication. 

 Falk, G. (1955). Amer. J. Physiol, 181, 157. 

 Heller, H. (1952). J. Endocrin., 8, 214. 



Heller, H., and Stephenson, R. P. (1950). Nature, Lond., 165, 189. 

 Krecek, J., and KreCkova, J. (1957). Physiol. Bohemoslov., 6, 26. 

 Krecek, J., Kreckova, J., and Dlouha, H. (1956). Physiol. Bohemo- 



slov., 5, suppl., p. 35. 

 RiCHTER, C. p. (1936). Amer. J. Physiol, 115, 155. 

 Sawyer, W. H. (1952). Amer. J. Physiol, 169, 583. 

 ScHAUMANN, O. (1949). Experientia, 5, 360. 

 Young, P. T. (1949). Comp. Psychol Monogr., 19, No. 5, 1. 

 Young, P. T., and Chaplin, J. P. (1949). Comp. Psychol Monogr., 19, 



No. 5, 45. 



[Discussion of this paper was postponed until after the paper by Dr. 

 Desaulles. — Eds.] 



