THE SECRETION OF URINE 



477 



The work may be performed in an excretory direction or in an 

 absorptive direction. For instance, to concentrate through a semi- 

 permeable membrane the urine from the chloride content of the blood 

 (0-38 per cent.) to that of normal urine (0-8 per cent.) requires 

 the expenditure of a large amount of work on the part of the kidney 

 cells. It would also require a large expenditure of work to separate, 

 as after large libations, a urine consisting of little more than water. 



The questions in dispute, then, at the present time are these: 

 (1) Is the work of the kidney performed in actively secreting sub- 

 stances in the glomeralus and in the tubules ? or (2) is it secreting 

 in the tubules only ? or (3) is the work performed in concentrating 

 urine in the tubules ? or (4) is it concerned in all these processes ? 



0-1 H 



005- 



Ringer-Solution. 



FIG. 232. 

 Line = oxygen consumption; black area = urine excreted. (Barcroft and Straub.) 



Valuable evidence has been adduced by the study of the action, 

 upon the internal respiration of the kidney, of various substances, 

 such as sodium chloride, Ringer's solution, urea, caffeine, and sodium 

 sulphate substances which stimulate the flow of urine, and act as 

 diuretics. The last three substances, when injected into the blood, 

 cause a diuresis which is attended by a markedly increased absorption 

 of oxygen; 5 percent, sodium chloride and Ringer's solution, on the 

 other hand, cause a diuresis which is unattended by any such increased 

 oxygen absorption (Fig. 232). When the kidney cells have been 

 poisoned by mercuric chloride, the oxygen consumption of the kidney 

 almost stops. Sodium sulphate is then practically without action in 



