The Excretion of Urea. 



59 



transparent. The medullary substance is at first arranged in a 

 series of beaded threads running parallel to the long axis of the 

 sheath, the threads undergoing a progressive side by side fusion, 

 until eventually all merge into a single axial core for each of the 

 now considerably elongated sheaths. This Cajal method, though 

 notoriously capricious with the Golgi apparatus, gives some result 

 for the present purpose in perhaps 75 per cent, of trials. 



34 (1494) 



The excretion of urea. 



By J. H. Austin, Edgar Stillman and D. D. Van Slyke. 



[From the Hospital of The Rockefeller Institute for Medical Research, 



New York.] 



The excretion rate of urea in normal men increases directly as 

 the blood urea concentration, and as the square root of the volume 

 of urine, so long as the latter remains within ordinary limits, 

 under about 5 liters per day. These relations are expressed in the 

 formula, D = KB^lV, D representing the rate of urea excretion, 

 calculated as grams per 24 hours, B the blood urea concentration 

 (grams per liter), V the rate of urine excretion, calculated as liters 

 per 24 hours. When the size of the individual (W = weight 



D IV 



in kilos) is introduced the equation becomes — = KB yj^y, or 

 D 



K = — f= . K = 7.5 ± 3 for normal individuals. When de- 

 B^iVW 



ficiency of the urea-excreting function is present K has a lower 

 value. Increase in volume output beyond the rate of about 200 

 c.c. per hour, or 5 liters per 24 hours, ceases to accelerate urea 

 excretion, so that for volumes of V in excess of 5, the figure 5 may 

 be inserted in place of the actual V. The above formula gives 

 more consistent results than that of Ambard, which assumes 

 erroneously that the excretion rate increases as the square rather 

 than the first power of the blood urea ; and correlates the excretion 

 with the concentration of the urea in the urine rather than with 

 the volume of the urine. In calculating the rate of urine and urea 

 output from short time periods, errors occasionally occur from 



