354 HERMAN O. MOSENTHAL 



Another element that militates against the linking of clinical observa- 

 tion with the site of the renal anatomical lesion, is the lack of an accurate 

 knowledge of kidney physiology. This is a problem which still remains 

 in the clutches of theory and is not a realization. Bowman believed that 

 the glomeruli excreted water and the tubules the urinary solids ; Ludwig's 

 (&) idea was that all the urinary constituents originated in the glomeruli 

 by filtration and that concentration was brought about by absorption of 

 water in the tubules; Cushny's(6) "modern theory" is somewhat similar: 

 first, there is a purely physical filtration through the glomeruli of all the 

 constituents of the plasma except the colloids, and, secondly, there is a re- 

 sorption by the vital activity of the tubules, which modifies the filtrate so 

 that it forms the urine ultimately excreted. Even a superficial acquaint- 

 ance with the histology of the kidney would indicate that the water of the 

 urine must originate in the glomeruli ; the question of how the solids pass 

 out of the kidney is another matter. The conception of reabsorption of 

 water by the tubules is ingenious but has to be regarded as purely theoret- 

 ical. Recently, Oliver has conclusively shown that there is an active secre- 

 tion of urea by the proximal convoluted tubules and that this secretion is 

 added to the urea which passes through the glomerular filter with the other 

 crystalloids of the blood plasma. This observation confirms the findings of 

 various workers that dyes, uranium, phosphates, urea, uric acid and salt 

 may be excreted by the tubules. This fact is important because it indi- 

 cates that the tubules play a very active role in the excretion of the body's 

 waste products and not a negligible one, as they would if their sole func- 

 tion were to absorb water from the glomerular filtrate. 



Even conceding that a fairly satisfactory theory of renal physiology 

 has been developed, it becomes very difficult to apply this to the interpreta- 

 tion of clinical tests. The following examples may make this statement a 

 little clearer: should the glomeruli cease to function because they are in- 

 flamed, congested, or because of lack of fluid supply, etc., the tubular ac- 

 tivity must necessarily be suspended since there is no water to carry away 

 the products which they eliminate; should the tubules become obliterated 

 by pressure in the interstitial spaces as in congestion, or blocked by the 

 accumulation of debris resulting from degenerative or inflammatory prod- 

 ucts within them, evidence of function of the corresponding glomeruli 

 must necessarily be lacking for the material excreted by them can not pass 

 on to the collecting tubules. A recent observation of Richards, that, in the 

 frog at least, not all of the glomeruli are functionating all the time, but 

 that they have quiescent periods, opens up many obvious possibilities that 

 may inject new aspects into the perplexities of interpreting renal func- 

 tional tests properly. 



From what has been said in the last three paragraphs, it becomes evi- 

 dent that tests for renal function can not be regarded solely in the light of 

 renal pathology, nor can they be valued as a sign of existing function 



