MECHANISM OF RENAL SECRETION 35 



as urine is by no means serum minus its albuminoid bodies 

 (Sobieranski (10)). 



The basic possibilities of a mechanism of renal secretion fall 

 therefore under two main opposing views. The one places on 

 the malpighian body the function of secreting or filtering by 

 far the greater portion of the urine, which is later supposedly 

 concentrated on its passage downward by reabsorption of the 

 excess of water. On the other hand, the opposing view states 

 that the concentration of the urine as it passes through the 

 tubules is the result of secretion of salts and organic constituents 

 into the lumen by the cells of the convoluted tubules. There is 

 a third possibility to be considered, namely, that both mechan- 

 isms may play a role and are in a sense in equihbrium with each 

 other. 



The literature on experimental and anatomic evidence in 

 connection with the mechanism of renal function is exceedingly 

 voluminous. Most of the work that has been done can be class- 

 ified under three general headings: Those studies dealing with 

 the total renal function and the general effects of altered condi- 

 tions; secondly, those pertaining to the function of the various 

 units of the uriniferous apparatus and the localization of func- 

 tion, and, thirdly, the functional alterations occurring with 

 distinct renal pathology. As examples of the first group of 

 experiments there are the studies of salt concentration under 

 varying conditions, the effects of diuretic stimulation (10), vary- 

 ing intraureteral pressures (11, 12), and variations in blood pres- 

 sure and vascular supply (6, p. 99; 13). The localized studies on 

 the function of the various elements of the uriniferous system 

 concern us more in this paper. Among these investigations 

 Nussbaum's justly famous work (15) of partially obliterating 

 the circulation of the frog's kidney and noting the effect upon 

 urine formation is perhaps the earliest which clearly recognizes 

 the necessity for obtaining evidence of local function instead of 

 studying the organ as a whole, as the function of the organ is 

 nothing more than the composite function of its parts. Con- 

 siderable work along similar, but modified, lines has been done 

 since (16, 17). The work of Nussbaum and others is defective 



