362 HERMAN O. MOSENTHAL 



concentration of urea in the urine. Hence Ambard's second law (see 

 section on Ambard's constant) is not correct in the view of later researches. 



The Reliability of Coefficients of Urea Excretion. Jonas and Austin 

 express their skepticism concerning the precision of the Ambard coefficient. 

 In the later constant of Austin, Stillman and Van Slyke, the most obvious 

 mistakes of Ambard's work have been corrected. However, even these 

 recent investigators, in elucidating their improved equation, tell us that 

 other factors than those represented in their formula may modify the 

 value of the constant. They mention "nervous" or "hormone" influ- 

 ences. It is undoubtedly true that no test, applied to human function, pos- 

 sesses absolute mathematical accuracy. It will always require a great 

 deal of clinical judgment and experience to properly evaluate any pro- 

 cedure of this sort. That the coefficient of urea excretion is particularly 

 susceptible to influences for which no allowances can be made in a routine 

 formula is very obvious. 



Method of Determining the Coefficient of Urea Excretion. A time 

 is chosen which is as long as possible after the ingestion of food. This 

 will tend to produce a comparatively constant level of urea in the blood. 

 The patient drinks about 200 c.c. of water in order to insure an adequate 

 flow of urine ; one-half hour later, the bladder is emptied and the urine 

 subsequently collected after an accurately timed interval. This should 

 not be longer than two hours, and by preference this period should be 

 shorter. The blood is collected midway between the two voidings that 

 demark the urinary specimen which is to be analyzed. The urea is de- 

 termined in the blood and urine; the urine is measured and calculations 

 are made to increase it to a 24 hour basis ; the figures are then substituted 

 in the formulas previously given and the coefficient obtained. 



The Clinical Value of the Coefficient of Urea Excretion. Thus far 

 the application of the coefficient to patients has only been with Ambard's 

 constant or its modification, the McLean Index. Hence the conclusions 

 which follow have no other basis. The urea-secretory constant of Austin, 

 Stillman and Van Slyke awaits its clinical christening. 



In general the coefficient of urea excretion may be regarded as paral- 

 leling the progress of acute or chronic renal disease fairly well; it seems 

 to fall in line, in the majority of cases, with the phthalein test. Its main 

 point of value appears to be that in those cases with impaired kidney 

 function that have their blood urea reduced to a normal level, the coeffi- 

 cient will nevertheless show subnormal values and thus indicate the true 

 state of aft'airs (Lewis, McLean (a), Ambard, and Widal, Weill and Val- 

 lery-Radot). On the other hand, Jonas and Austin believe that this 

 method of testing renal function affords "no information of diagnostic or 

 prognostic value that could not be as readily deduced from the blood urea 

 alone." This is true to a certain degree. Whether the new "urea-secre- 

 tory constant" will obviate some of the faults in the older formula re- 



