997 
slight variations of the chemical composition of the circulation fluid, 
but also on slight differences of temperature. Thus this simple 
membrane forms a nice object for quantitative studies on permeability 
under various physiological conditions. 
January 1917. Physiological Laboratory, Groningen. 
Physiology. — ‘“Heperimental researches on the permeability of 
the kidneys to glucose’. By Prof. H. J. HAMBURGER and 
R. BRINKMAN. 
II. THE POTASSIUM REQUIRED IN THE CIRCULATING-FLUID IS 
REPLACED BY URANIUM AND RADIUM. 
(Communicated in the meeting of January 27, 1917) 
From our preceding paper it appeared that if a Rinexr-fluid con- 
taining glucose and composed of NaCl 0.7°/,, NaHCO, 0.02°/,, KCl 
0.01.°/,, CaCl, 0.0075 °/, was circulated through a frog’s kidney, 
0.03 °/, of glucose was retained. Now ZWAARDEMAKER and FpENSTRA 
availing themselves of the conclusions arrived at by N. R. CAMPBELL 
that potassium is the only radio-active element found in the body, 
have discovered that in the RiNerr-fluid which maintains the beating 
of the heart, potassium may be replaced by uranium, radium and 
thorium and that in equivadioactive doses*). It seemed of importance 
to us to determine whether in the above-mentioned circulating-fluid 
this substitution may likewise be effected with regard to the kidney. 
Can here too uranium and radium take the place of potassium 
and if so in what proportion, in a molecular or in a radioactive one? 
Hence the KCl in the RiNeer-fluid which contained 100 milli- 
grammes of KCl per litre was replaced by the equiradio-active 
quantity; viz. 15 milligrammes of U(NO,), per litre. And it was indeed 
found that here too the maximum quantity of glucose was retained. 
If, however, instead of 15 milligrammes of nitrate of uranium, 25 
milligrammes are added, only very little glucose is retained. If the 
litre of RiNerr-flnid without K, contains 35 mGr. of U(NO,),, no 
glucose is retained at all. 
Now 100 m.Gr. of KCl are chemically equivalent with 112 m.Gr. 
1) These Proceedings Vol. XIX p. 99, XX 341 and 633. 
Compare also ZWAARDEMAKER, FEENSTRA and BENJAMINs, ibid. Nov. 10 1916. 
