ON PHYSICO-CHEMICAL METHODS AND PROBLEMS. 2l 



poses the work of the kidneys as determined in this way 

 have failed. 



It seems to me that still another point should be noted. 

 It is readily apparent when one studies the papers that 

 have followed DRESER'S initiative that the method of 

 measuring the work of the kidneys as criticised above 

 has been regarded as giving the value of the to tal work 

 done. At the best, however, the method determines 

 only that portion of the work which is necessary to bring 

 about the secretion of the water of the urine. For our 

 urine does not represent a concentrated or a diluted 

 blood, but contains, as we know, the constituents of the 

 blood in different concentrations, even when we disregard 

 the osmotically inactive substances (albumin). 



If we imagine a certain amount of urine having the 

 same freezing-point as the blood, separated from this 

 by a thin permeable membrane, and the blood kept in 

 circulation and maintaining its original composition as 

 in the body, an interchange between the diffusible con- 

 stituents of the urine and those of the blood takes place 

 until the amount of these is the same on both sides of the 

 membrane. We will call such an interchange a molecular 

 interchange, as does KORANYI, because the molecular 

 concentration of the two fluids remains the same through- 

 out the experiment. As we do not have to do in this 

 case with differences in osmotic pressure, the external 

 work is zero. But a certain amount of internal work 

 is performed, the direction of which can also be deter- 

 mined.- For substances migrate from regions having a 

 higher concentration to those having a lower one, through 

 which a certain amount of osmotic work becomes free 

 for each of the substances. The sum of all these different 



