396 Transactions of the Canadian Institute [vol. ix 



argument for the normal character of the result is that in the same section 

 the regions of the convoluted tubules and Henle's loops show the localiza- 

 tion while the region of the collecting tubules do not. If it were due to 

 an artefact occasioned in the freezing or subsequent treatment the whole 

 section would be uniform. Again, there is the fact that in many tubules 

 where a cut and an uncut surface can be distinguished, the uncut surface 

 will show the potassium deposit while the cut section will be entirely 

 free. Further, those tubules that evidence the localization are as a rule 

 more heavily stained by the reagent than those that do not exhibit it, 

 thus showing that the protoplasm in the two instances must differ in 

 some respect. 



Discussion, 



Special attention was drawn by Professor Macallum^ two years ago to 

 the various suggestions that surface tension might play a part in different 

 processes of the living organism. He has discussed these suggestions 

 and expanded them to apply to cellular activity in general. In any 

 attempt to relate surface tension to renal function one must bear in 

 mind that protoplasm is of more or less colloidal nature, and also that it 

 is living material. What factors modifying the ordinary forces of sur- 

 face tension this introduces have not been fully investigated, but, as 

 surface tension appears to be involved in renal secretion, a discussion of 

 its action in relation thereto may be permitted. 



The kidney cells, whether considered individually or collectively 

 in the tubule, form peripherally a system with lymph-cytoplasm inter- 

 faces, a condition somewhat analogous to a liquid-liquid interface, the 

 two liquids forming the latter differing greatly in density. Centrally, 

 if the lumen be filled with fluid, a cytoplasm-fluid interface would result, 

 though if the tubule were collapsed this would not obtain. Now in a 

 drop of liquid surrounded by air, organic substances lower the surface 

 tension, while most inorganic solutes raise it. Hence in accordance with 

 the law that energy tends ever to a minimum in a system, the organic 

 solute is found concentrated at the surface of the drop, while the inoiganic 

 solute is more dilute at the surface as compared with the interior of the 

 drop. Thi? is called the Gibbs-Thomson principle, and had been 

 expressed mathematically in a formula deduced by Gibbs for the con- 

 centration of one of the phases at an interface separating a two-phase 

 system. When, however, the drop is in contact with another fluid with 

 which it does not mix or is in contact with a solid (e.g., glass), the surface 

 tension of the drop on the contact surface is greatly ( iminished and, in 

 consequence, there the solutes condense whether they ordinarily tend to 



