20 PHYSICAL CHEMISTRY IN MEDICINE. 



determine from it, by freezing-point determinations, only 

 the difference between these two values, while the kidney 

 has in reality performed the sum of the two. All the 

 measurements of osmotic renal activity made by DRESER 

 do not take this important fact into consideration. Failure 

 to consider it must of necessity lead to radically incorrect 

 conclusions. 



The normal human being usually secretes a urine the 

 freezing-point of which is lower than that of the blood, 

 because its molecular concentration is greater. By con- 

 suming much water we are, however, able to raise the 

 freezing-point of our urine, and it would not be difficult 

 to so regulate by artificial means the amount of water 

 taken up by the organism that the freezing-point of urine 

 and blood would be the same. If now we base our cal- 

 culation of renal work upon the difference between the' 

 freezing-point of the blood and that of the urine, a 

 difference which under these circumstances would be 

 zero, then we would be compelled to conclude that the 

 secretion of a urine equimolecular with that of the blood 

 had been accomplished without work, while as an actual 

 matter of fact it may have demanded a great deal of 

 work. For after what has been said it is clear that the 

 osmotic work of water secretion and the osmotic work of 

 water absorption by the kidneys equal each other in this 

 case. 



A statement which is found in various articles and which 

 threatens to be adopted by text-books, that the work per- 

 formed by the kidneys in twenty-four hours normally 

 varies between 70 and 240 kilogrammeters, has therefore 

 no real value. After what has been said it will not seem 

 strange that the attempts to utilize for diagnostic pur- 



