1913.] Experiments on the Kidneys of the Frog. 363 



Table III. 



Expt. 



Concentration of urine. 



Concentration perfusing 

 fluid. 



Normal kidney. 



Glomeruli killed. 



1 



2 



3 

 4 



f (a) -48 per cent. NaCl 

 1(4) 0-45 „ 

 f(a) 0-43 „ „ 

 \ (b) 0-34 „ 

 [(c) 0-33 „ 

 J (a) 0-48 „ 

 I (b) -38 „ 

 J (a) 0-46 „ 

 1(4) 0-36 „ 



f (a) -45 per cent. NaCl 

 \(b) 45 „ 



0-36 „ ' „ 



f (a) -42 „ 

 \(b) 43 „ 

 J (<*) -48 „ 

 t (b) -48 „ 



-56 per cent. NaCl 



0-55 „ 

 50 „ 

 -53 „ 



In all the experiments the perfusing fluid contained sodium chloride plus '02 per cent. KC1 

 • and - 03 per cent. CaCl 2 . The letters (a) and (b) refer to separate samples of urine. 



(c) Caffein, — Barcroft and Straub have shown that caffein sodium benzoate 

 greatly diminishes the consumption of oxygen by the mammalian kidney, 

 and they used it for the purpose of poisoning the renal tubules. We have 

 carried out a number of experiments to determine the action of caffein on 

 the frog's kidney. In our early experiments 1 per cent, caffein sodium 

 benzoate was perfused through the renal portal veins for five minutes, the- 

 arterial perfusion of oxygenated Ringer's solution being simultaneously 

 maintained ; the collection and examination of the urine was not begun until 

 from one to two hours after the perfusion of the caffein, and it was found to- 

 be hypotonic to the perfusing fluid. At that time we believed that caffein. 

 (in the dose given) permanently poisoned the tubules, and we therefore 

 regarded the glomeruli as capable of secreting a hypotonic urine. Further 

 experiment seems to show, however, that the poisoning effect of caffein is merely 

 temporary. The immediate effect is to render the urine isotonic with the 



Table IV. — Action of Caffein Sodium Benzoate. 



Expt. 



Concentration of fluid in terms of NaCl. 



Perfusing fluid. 



Normal urine. 



Urine after poisoning tubules with 

 caffein 



Immediately after. 



1-2 hours after. 



1 



2 

 3 



per cent. 

 0-53 

 0-55 

 0-51 



per cent. 

 25 

 0-40 



iper cent. 

 0-54 

 55 



per cent. 

 0-22, 0-30 



