398 Transactions of the Canadian Institute [vol. ix 



When we consider that only a portipn of the kidney is active at one time 

 we see the energy expenditure, if expressed as surface units, would appear 

 very ample for excretory purposes. 



As found in the preparations referred to, the potassium is localized 

 on the periphery of the excreting portion of each tubule and in the 

 cytoplasm of the cells forming it. As indicated above, the peripheral 

 deposit can be explained only as condensation, due to surface tension, 

 from the lymph bathing the surface of the tubule. This condensation 

 effect would involve also the sodium, magnesium and calcium salts and 

 the metabolites, such as urea and uric acid, and if there were a micro- 

 chemical reaction for each of these as sensitive as the one employed for 

 potassium the application of it would probably show such a condensation 

 layer, although perhaps in every case not to the degree illustrated by 

 the potassium preparations. The results of Lewis' estimations of the 

 concentration of the condensation layers of different compounds from 

 their solutions on the surface of droplets of paraffin oil rising or of mercury 

 falling through such solutions seem to indicate very distinctly that the 

 concentrations may greatly exceed the proportions postulated by the con- 

 centrations in the solutions, and, as already pointed out, this is specially 

 the case with potassium salts. We might, therefore, expect the respec- 

 tive concentrations of the salts and metabolites on the external surface 

 of each excreting tubule to exceed very greatly their concentrations in 

 the lymph. 



It is not unreasonable to suppose that the basal surface of each 

 excreting renal cell, on which the condensation has occurred, is per- ^ 

 meable to the constituents of the deposit. The entrance of potassium 

 and other salts into the cell would bring them into a new system in which 

 their distribution would be affected by the surface tension of the cell as 

 a whole and of its individual parts. In consequence, condensations 

 would occur, and particularly on interfaces and surfaces where the surface 

 tension is very low. In fluids this condensation occurs quickly, but it is 

 possible that in a colloidal system, such as the renal cell illustrates, the 

 condensation might not be effected so quickly, and yet it would occur 

 with such rapidity as to keep down the concentration in the cytoplasm 

 generally. 



The occurrence of a condensation of potassium salt in the cytoplasm 

 of the renal cell immediately adjacent to the lumen of the tubule would 

 seem to indicate that this border of the cell has a low surface tension as 

 compared with the other surfaces of the cell, and especially with the 

 basal one, and, consequently, other salts than those of potassium would 

 be condensed there also. This difference in surface tension could only 

 be maintained by a constant expenditure of energy in the cell, and 



