The call for oxygen considered as a physiological test 115 



therefore to test the matter for ourselves and find out if possible the 

 limits within which this statement is true. It is clear at the outset 

 that, while it may be perfectly true that such a kidney does not 

 secrete, it is quite a different matter to suppose that it cannot be 

 made to do so by appropriate methods. 



We first tested the matter with Ringer's fluid and with sodium 

 chloride on the one hand, these being diuretics which can act 

 mechanically and elicit no call for oxygen. In contradistinction to 

 these we used caffeine, this being as we have already seen a diuretic 

 which acts solely in virtue of its stimulating effect upon the epithelium 

 of the kidney and has no salt effect. The result was perfectly clear 

 after asphyxiation of the cells of the kidney by clamping ; the sodium 

 chloride produced a copious diuresis, the caffeine on the other hand 

 produced no diuresis whatever. 



The following data are those of three experiments in which 

 diuresis was evoked, in the case of Exps. 1 and 2 by injection of 

 Ringer's fluid, in the case of Exp. 3 by injection of 10 c.c. of 5 per 

 cent, sodium chloride, the animal in each case being a rabbit. 



It is clear that any diminution which takes place in the diuresis 

 is amply accounted for by the less satisfactory vascular condition, 

 and in any case there is in each experiment a good diuresis after the 

 artery has been clamped for periods varying from 10 seconds to 

 18 minutes. 



On the other hand the following experiment will show how different 

 is the effect of clamping upon the diuresis obtained by caffeine : 



82 



