66 DONALD D. VAN SLYKE 



salt, 20 per cent as the acid salt. Consequently whatever phosphate above 

 20 per cent of the total is excreted as BH 2 PO 4 represents acid removed 

 from the body. At pH 4.8 99 per cent is in the form of the acid salt. 

 It is therefore possible for a gram molecule of excreted phosphate to 

 represent a maximum of 0.79 gram equivalents of acid removed from 

 the body. 



P-hydroxybutyric acid, of which the acid dissociation constant is 

 2 X 10~ 5 (Henderson and Spiro, 1909) is excreted at pH 4.8 to the 

 extent of 55 per cent as the free acid, whereas in the blood it is practically 

 100 per cent in the form of alkali salt. Therefore it is possible for a gram 

 molecule of excreted beta-hydroxy butyric acid to represent 0.55 gram 

 equivalents of acid removed from the body. 



The most logical measure of the amount of excreted acid is the 

 amount which is determined by titrating the urine with alkali from its 

 observed pH to pH 7.4 (Henderson and Palmer, 1914). The amount 

 usually thus excreted by an adult is 200-400 c.c. of N/10 acid per 24 

 hours. Acid excretion appears to increase when a fall occurs in either 

 blood pH or alkali reserve. When the blood pH is reduced, the acid 

 excretion increases, even though the fall in pH be due to CO 2 excess, and 

 without reduction in the total buffer alkali of the blood (Davies, Haldane, 

 and Kennaway, 1920). Also, however, when the blood pH is normal, 

 but the BHCO 3 has been lowered, as in compensated diabetic acidosis, the 

 acid excretion is increased in the apparent attempt to raise the alkali 

 reserve back to its normal level. The excretion of free acid may in such 

 cases rise to as high as 1,000 c.c. of decinormal acid per twenty-four 

 hours. 



4. The Formation of Ammonia. Even more important, in man, for 

 restoring the available alkali of the body than the excretion of free acid 

 is the formation of ammonia. The proportion of urinary nitrogen excreted 

 as ammonia is normally about 5 per cent, and the amount 300 to 500 c.c. 

 of 0,1 N NH 3 per 24 hours.. In severe diabetic acidosis it may be 10-fold 

 as great. 



Ammonia formation rises, like acid excretion, in response to a fall in 

 either blood pH or alkali reserve. It appears to be fairly proportional 

 to the amount of acid metabolites formed, exclusive of acid phosphate. 

 This is peculiar among the acid products in that it is excreted almost 

 entirely as free acid, H(BHPO 4 ), and does not stimulate ammonia forma- 

 tion (Marriott and Howland, 1916). The highest ammonia excretions 

 clinically observed have been seen in diabetic ketonuria, where the excre- 

 tion may reach 5,000 c.c. of N/10 NH 3 per day. It can, therefore, rise 

 to a height several times greater than the excretion of free acid. 



The sum, ammonia plus titratable acid, bears a sufficiently close rela- 

 tion to the blood bicarbonate to be used as a rough measure of the latter 



