ON PHYSICO-CHEMICAL METHODS AND PROBLEMS. 19 



The amount of water given off can be readily calcu- 

 lated: it is the amount which must be separated from 

 the urine in order to change this into a liquid having the 

 high molecular concentration of the blood. 



The calculation of the work necessary to accomplish 

 this is, however, not as simple as DRESER believes, since 

 through the transport of the water from the blood to the 

 urine the concentration of the latter is steadily altered, 

 a fact which this author has not taken into consideration. 



We will look upon the amount of work necessary for 

 this purpose, which can be determined mathematically 

 as a measure of the water-secretory function of the kidneys. 



The converse of the above would exist when the kidney 

 has to prepare, from a liquid having the osmotic pressure 

 of the blood, one having a molecular concentration 

 greater than the blood. Under these conditions we 

 should have to add a certain amount of water to the urine 

 in order to make its osmotic pressure equal to that of the 

 blood. While in the first case, therefore, the kidneys 

 have to express water from the blood, this time they 

 have to express it from the urine and return it to the 

 blood. 



The work corresponding to this, which has been cor- 

 rectly determined by DRESER, we will have to regard as 

 a measure of the water-absorption activity of the kidneys. 



As we know from numerous facts, this double function 

 of the kidney is performed by two different parts of the 

 organ. While the glomeruli probably secrete the water 

 of the urine, the uriniferous tubules have an antagonistic 

 function. 



The urine which we are able to examine has already 

 been subjected to both kinds of work. We are able to 



