498 



SCIENCE 



[N. S. Vol. XXXII. No. 824 



of the tubule. In these cells the potassium 

 injected into the lymph circulation is being 

 ■excreted, and the condensation of the ele- 

 ment at or near the surface of the lumen 

 is evidence that there the tension is less 

 than at the other extremity of the cell. 



These facts are in their significance in 

 line with some observations that I have 

 made on the absorption of soluble salts by 

 the intestinal mucosa in the guinea-pig. 

 When the "peptonate" of iron was admin- 

 istered in the food of the animal it was not 

 unusual to find that in the epithelial cells 

 of the villi the iron salt was distributed 

 through the cytoplasm, but its concentra- 

 tion, as a rule, was greatest in the cyto- 

 plasm adjacent to the inner surface of the 

 cell, from which it diffused into the under- 

 lying tissue. Here also, inferentially, sur- 

 face tension is lower than elsewhere in the 

 cell. 



It would perhaps be unwise to form final 

 conclusions at this stage in the progress of 

 the investigation of the subject, but the 

 results so far gained tempt one to adopt 

 as a working hypothesis that in the secre- 

 ting or the excreting cell lower surface 

 tension exists at its secreting or excreting 

 surface than at any other point on the cell 

 surface. How this low surface tension is 

 caused or maintained it is impossible to say, 

 but, whatever the solution of the question 

 may be, it is important to note that we 

 must postulate the participation of this 

 force in renal excretion in order to explain 

 the formation of urines of high concentra- 

 tion. These have a high osmotic pressure, 

 as measured by the depression of the freez- 

 ing-point, while the osmotic pressure of the 

 blood plasma determined in the same way 

 is low. On the principle of osmosis alone, 

 as it is currently understood, this result is 

 inexplicable, for the kinetic energy, as re- 

 quired in the gas theory of solutions, 

 should not be greater, though it might be 



less, in the urine than in the blood. It is 

 manifest that in the formation of concen- 

 trated urines energy is expended. We 

 know also from the investigations of Bar- 

 croft and Brodie that the kidney during 

 diuresis absorbs much more oxygen per 

 gram weight than the body generally, and 

 that, assuming it is used in the combustion 

 of a proteid, a very large amount of energy 

 is set free, very much more, indeed, than is 

 necessary. It has also been observed that 

 a portion of the energy set free is found in 

 a higher temperature in the excretion than 

 obtains in the blood itself circulating 

 through the kidney. This large expendi- 

 ture of energy is, probably, a result of the 

 physiological adaptation of the principle 

 of the ' ' factor of safety, ' ' which, as Meltzer 

 has pointed out, occurs in other organs of 

 the body. 



In cell and nuclear division surface ten- 

 sion Operates as a force, the action of which 

 can not be completely understood till we 

 know more of the part played by the cen- 

 trosomes and centrosphere. That this force 

 takes part in cell reproduction has already 

 been suggested by Brailsford Robertson. 

 He has devised an ingenious experiment to 

 illustrate its action. If a thread moistened 

 with a solution of a base is laid across a 

 drop of oil in which is dissolved some free 

 fatty acid the drop divides along the line 

 of the thread. When the latter is moist- 

 ened with soap the drop divides in the same 

 way and in the same plane. The soap 

 formed in one case and present in the other, 

 it is explained, lowers the surface tension 

 in the equatorial plane of the drop, and 

 this diminution results in streaming move- 

 ment away from that plane which bring 

 about the division. He suggests that in 

 cell division there is a liberation of soaps 

 in the plane of division which set up 

 streaming movements from that plane to- 



