34 E. J. STIEGLITZ 



Bowman (1) in his memorable paper on the activity of the 

 malpighian body in 1842, first conceived the idea that water and 

 salts entered the urine from the blood through the squamous 

 epithelium surrounding the glomerulus and that the organic 

 substances of the urine were secreted by the convoluted tubules. 

 This theory, greatly supported by the researches of Heidenhain 

 (2, 3, 4) on the passage into the urine of sulphindigotate of 

 soda, is in direct opposition to the conception postulated by 

 Ludwig (5, 14) ('43), and now largely supported in a much 

 altered form by Cushny. This theory in its original state 

 assumed that water and salts, and, in fact, all the urinary con- 

 stituents, passed through the malpighian body in the form of a 

 dilute filtrate, which, as it passed down the uriniferous tubules, 

 was concentrated by the reabsorption of water by the cells lining 

 these tubules. At present, the theory, as modified and expanded 

 by Cushny (6), includes the reabsorption of certain of the salt 

 constituents which form the 'threshold bodies.' Of these bodies 

 sodium chloride is perhaps the best example. It appears in 

 the urine only when its concentration in the blood stream is 

 above a specific level. In other words, there is a limit at which 

 its elimination stops, the physiologic threshold. It is supposed 

 by Cushny that this threshold is maintained to some degree by 

 the reabsorptive activity of the cells of the convoluted tubules; 

 he points out that such substances as belong to this group appear 

 to be essentials in metabolic economy. Cushny (6, p. 50) con- 

 ceives the two processes, that of glomerular filtration and tubu- 

 lar reabsorption, as being independent, but coordinated by the 

 related common blood supply and by the rapidity of flow down 

 the tubule. The last-named factor he deems especially impor- 

 tant in connection with diuresis. 



Kliss (7) in 1881 suggested an amplification of the theory of 

 Ludwig, namely, that the filtrate which came through the 

 glomerulus was nothing less than blood serum in the form of a 

 transudate, and that under normal conditions the serum albu- 

 min and globulin and other protein constituents were removed 

 by the convoluted tubules. Despite the supporting observations 

 of Posner (8) and Ribbert (9), this conception must be discarded, 



