1. The water and electrolyte changes in the uteri of spayed rats have been investigated after the administration of oestradiol-17 (\g=b\) and are found to fall into two main phases.2. 6\p=m-\10 hr. after the subcutaneous injection of the hormone the total water content increases, as a result of expansion of the extracellular fluid space and of the relative cell volume. The increase of the relative cell volume is caused by an increase of the idiomolar value.3. 18\p=m-\54 hr. after the injection the total water content increases again after a temporary fall. The water increase is now confined to the intracellular space. Total nucleoprotein and residual phosphorus increase, and it is suggested that the nucleoprotein phosphate groups are responsible for the increase of the electrostatic equivalent and hence the increased potassium concentration in the cells. The idiomolar value falls, and there is probably an increased formation of cell protein at this stage.

The chemical composition of the liver and skeletal muscle in rats which had been treated with 1\m=.\0\g=m\g. oestradiol has been investigated. The water and electrolyte content, creatine and creatinine phosphorus fractions and total nucleoproteins were studied. The changes in the water content are reciprocal to those already described for the uterus. The creatine and creatinine content and the total nucleic acid do not change significantly. There is an increase of the acid-soluble phosphorus in the first phase of the water increase in skeletal muscle which is related to some of the changes of intracellular potassium. In the liver there is an increase of the total water content between 28 and 36 hr. after injection, which is also associated with changes of acid-soluble phosphorus and cell electrolytes.Zuckerman, Palmer & Hanson [1950] showed that the changes in skeletal muscle (gastrocnemius and triceps) were, in the main, reciprocal to those in the uterus, so far as the water content was concerned. The water content reached a peak between 18 and 24 hr., and at 54 hr. after the injection of oestrogen. Little appears to be known about the effects of this treatment on the water and electrolyte balance in the liver.The changes induced by oestradiol-17 (ß) in the water and electrolyte composition of the rat uterus have been reported in an earlier paper [Cole, 1950 c]. The investiga¬ tion has now been extended to skeletal muscle and liver, without altering the experimental procedure. MATERIAL AND METHODSMature female rats were spayed under ether anaesthesia 3 weeks before use and were always allowed free access to food and water. The animals were injected with 1-0 µg. oestradiol-17 (ß) subcutaneously and were killed at intervals of 0, 8, 18, 24, 36, 54 and 72 hr. after the injection. Determinations of the intravascular space, water and electrolyte distribution, creatine and creatinine, phosphate fractions and total nucleic acids were made after each of these intervals in accordance with the methods previously described [Cole, 1950a-c]. Six animals were used for each determination, and the mean for any determination shown in the table is therefore derived from six experimental values. RESULTSThe results are given in Tables 1-4. The differences between the groups of rats killed at different times are calculated with reference to the control group at zero time. The significance of the differences have been estimated by means of the 't' test. The quantity represented by V, the relative cell volume in Conway's terminology [Boyle & Con way, 1941], is also calculated with reference to the control series [Conway & Hingerty, 1946; Cole, 1950a, 6].

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