770 



pointed out that a notable antagonism exists between potassium and 

 uranium in such a sense that they mutually neutralize each other 

 when present in amounts of a certain ratio. I have demonstrated 

 that the coinciding calcium exerts an influence here, which naturally 

 led us to suppose that this it was that caused the summer-equilibria 

 and the winter-equilibria to be so differently located. Our supposition 

 proved to be right. To destroy the effect of both the uranium and 

 the potassium a relatively much smaller amount of uranium is 

 required in the circulating fluid in summer than in winter, although 

 the same amount of potassium is taken in either season, so that the 

 fluid is getting somewhat like the potassium-free circulating fluid 

 just described, which is used also in the intermediate experiments. 

 The equilibria looked for are always reached with a potassium-free 

 fluid preceding. 



The following figure shows the winter- and the summer-equilibria 

 between potassium and uranium. The first have been determined by 

 Mr. T. P. Feenstra, the second by Dr. S. de Boer. The character 

 of the curves is very much alike and both decline with the larger 

 doses more and more gently, running at last nearly parallel to the 

 abscisse. The addition of a very large quantity of potassium salt has 

 a disproportionately slighter effect than that of a much smaller dosis 

 of uranium-salt. As yet only uranyl compounds were at my disposal, 

 but no difference revealed itself here between the various salts 

 (nitrate, acetate, sulphate). 



Also the summer-equilibria between potassium and thorium and 

 those between rubidium and uranium have been established by us. 

 The curve of the counterbalanced concentrations runs, on the whole, 

 like the one in the figure below. 



aOxtTö:/ 



♦0- 



30- 



20- 



Antagonism Potassium Uranium. 



Winter 

 frogs. 



mer 



m n «F I I I t I t I t I I I I a I I »; I I 1 1 1 » I t viiiJXr. 



W •(OCceoMAU t«»(0 9a {too ao <{0 0O 90 500 10 



Fig. 7. 



