Appendix IV. Constant of Ambard 317 



APPENDIX IV. ON THE CONSTANT OF AMBAKD 



The determination of the Constant of Ambard (Ambard and Weill, Journal de 

 physiol. et path. gen. xiv, p. 73, 1914) is for the purpose of discovering whether 

 there is retention of urea or not. When the concentration of urea in urine is 

 25 grams per litre of urine, the concentration of urea in the blood (ur) divided by 

 the square root of the output of urea per 24 hours (Z>) is nearly constant, varying 



tJL 



between 6'3 and S'O, i.e. =- = ^(constant of Ambard). 



When the concentration of the urea in the urine is not 25 grams per litre but 

 C grams per litre, then D must be corrected for the change in concentration. It is 

 multiplied by the root of C and divided by the root of 25 ; this gives a factor termed 

 Z> 2r , which replaces D in the above equation, so that 



- = A'(constant of Ambard) 



and 



An actual observation does not last for 24 hours, but for a time T which is about 

 | of an hour, the volume of urine secreted in this time is v c.c. and the volume of 

 urine as calculated for the 24 hours at this rate of secretion is V, 



Jr rx24x60.. 



= Tooo^T Iltres ' 



the other measurements necessary are of course the concentration of urea in the 

 urine (7, and in the blood ur. If the final answer does not come between 8 and 6'03 

 the secretory action of the kidney is upset. 



