162 QUARTERLY JOURNAL OF MEDICINE 



to a definite test (urea concentration) being ascertained, while the blood urea and 

 the non-protein nitrogen are also examined. 



As regards the known relation of blood-pressure to the excretion of water, 

 Herringham (5) states that, broadly speaking, blood-pressure and amount of urine 

 vary together, though not from day to day in individual cases ; in disease the 

 quantity of urinary water does not vary so directly with blood-pressure as might 

 be expected. The urine may diminish while the pressure is steady, or the urine 

 may remain steady while the pressure falls. Such variations are not accounted 

 for by fresh access of local inflammation in the kidney, &c. ; they are ascribed to 

 local vascular changes. 



Deviations from the general relationship between height of general blood« 

 pressure and volume of urine are readily intelligible in view of what is known of 

 the occurrence of special alterations in the calibre of the renal vessels from 

 nervous or chemical influences, apart from or in addition to variations in aortic 

 pressure, as well as the effects of changes in the composition of the blood 

 (hydraemia, presence of diuretic constituents, &c.), such being capable of aflfecting 

 the water excretion without parallel change in aortic pressure. But in view of 

 the general relationship between blood-pressure and urinary volume it is, of 

 course, to be expected that the administration of nitrites should have decided 

 effects. 



Mason (16) has recently found that sodium nitrite alters the urinary volume 

 suflEiciently and frequently enough to warrant its withdrawal during a water test 

 for renal efficiency ; the effects on blood and urinary nitrogen were not described. 



There is no evidence of nitrites influencing kidney function otherwise than 

 through the vascular changes induced. It is evident that dilatation of the renal 

 vessels and the usual fall of general blood-pressure under nitrites act in different 

 directions on the flow of urine, the former tending to give increased transudation 

 or filtration, and the latter to diminish the excretion of water. Upon the relative 

 predominance of one or other of these two influences the urinary result will 

 naturally depend. 



The Method employed in the Study of the Renal Effi/iiemy of Cases ivith High 

 Blood-iyressure and of the same Gases umder the Influence of Vasodilators. 



On the first day of examination, breakfast was taken about 5 a.m. No food 

 or drink was allowed after this until after completion of the urea concentration 

 test on that day. 



About 9.30 a.m. to 10 a.m. at least 6 c.c. of blood were removed by puncture 

 of one of the veins over the anterior aspect of the elbow, and received into 

 a sterile test-tube containing a small quantity of powdered neutral potassium 

 oxalate. The blood was used for the estimation of the urea and non-protein 

 nitrogen. 



Immediately after the vein puncture, the bladder was emptied, and 15 gim. 

 of urea in 100 c.c. of water administered. 



Specimens of urine were obtained, with the exception of one or two cases, at 



