210 E. M. WiDDOwsoN AND R. A. McCance 



reach 100, because above pH 6-5 the excretion of titratable 

 acid falls more rapidly than the ammonia and is extinguished 

 before the excretion of ammonia, which continues at a de- 

 creasing rate up to pH 8. This tendency of the percentage to 

 rise as the pH of the urine goes above 6 • 5 is therefore exagger- 

 ated if the urines are titrated, as they mostly are nowadays, to 

 pH 7-4 instead of, as at one time, pH 8. 



Dihydrogen orthophosphates are the main buffer acids 

 which can be titrated in a normal adult's urine, but this may 

 not be so in disease if there is a great excess of abnormal 

 organic acids of the right buffer strength in the urine, such as 

 (3 -hydroxy butyric acid or amino acids. Apart from the 

 phosphates and weak organic acids which contribute by their 

 presence to the titratable acidity, the surplus of non-volatile 

 anions in the urine is very largely due to sulphates, derived 

 from the metabolism of protein (Hunt, 1956). Chlorides are 

 generally balanced by the equivalent amount of fixed base 

 unless calcium or ammonium chloride has been taken to 

 produce a chloride acidosis. 



The ability of the kidney to excrete hydrogen ions into the 

 tubules, and so to excrete the surplus non-volatile anions in 

 the way described, depends upon the activity of carbonic 

 anhydrase. Since it has been shown experimentally that the 

 degree to which the pH of the urine can be lowered depends 

 upon the activity of the carbonic anhydrase at any given time, 

 it may be that the lower and well-known limit of urinary pH 

 attainable by a normal person is an expression of the activity 

 of his carbonic anhydrase, but this is merely a suggestion at 

 the moment. 



The New-born Period and Later Infancy 



Complete collections of urine from three healthy baby boys 

 have been made for the first 48 hours of their lives, and again 

 over the whole of the 7th-8th day. These babies all passed 

 urine at the moment of birth and this was also collected. 

 Urine passed by two other babies at birth has also been 

 included in the series, and a 24-hour collection has been made 



