5CO PHYSIOLOGICAL CHEMISTRY 



on Metabolism. Consult text-books on physiological chemistry and 

 clinical diagnosis for complete discussion). The acidity of the urine 

 expressed in cubic centimeters N/io alkali required to neutralize the 

 24-hour output varies ordinarily from 200 to 500 under normal con- 

 ditions with an average of perhaps 350. It is dependent almost 

 entirely upon the diet, being low on a vegetable (base-forming) diet 

 and high on a diet containing much meat, rice, whole wheat products, 

 fruits containing benzoic acid, as prunes and cranberries, etc. (acid- 

 forming foods). On the administration. of 15 grams of sodium bicar- 

 bonate it may go down to 100; the ingestion of much acid-forming 

 food may increase it to 600. In fasting it may rise in a few days to 

 800. It must be borne in mind that acidities of less than 250 usually 

 indicate a true alkalinity of the urine inasmuch as phenolphthalein 

 changes in an alkaline solution. Samples of urine collected shortly 

 after a meal may be alkaline due to the so-called " alkaline tide." 



Bacterial decomposition of the urea of the urine occurring in the 

 urinary tract will increase the amount of ammonia and decrease the 

 acidity of the urine. The same change usually occurs in urine left in 

 contact with the air. The acidity of the urine is increased in acidosis, 

 cardio-renal and certain other disorders. The acidity of the urine 

 may be somewhat increased by administration of mineral acids, acid 

 phosphates, or benzpates, but it is much more difficult to increase than 

 to decrease this acidity. 



Van Slyke and Palmer 1 have suggested a method for the deter- 

 mination of organic acids in urine.- Inasmuch as organic acids other 

 than the acetone bodies are not excreted in significant amount in 

 diabetic acidosis this method may be used as an approximate estima- 

 tion of acetone bodies in diabetic urines. 



Hydrogen Ion Concentration or True Acidity 



Indicator Method (Henderson and Palmer's Adaptation of Soren- 

 sen's Method). 2 PrincipleThe reaction of the urine is estimated 

 by matching the colors produced when a few drops of indicator are added 

 respectively to the diluted urine and to standard solutions of known 

 reaction similarly diluted. Similar hydrogen ion concentrations 

 are indicated by similar colors. The indicator must be properly 

 chosen. 



Standard Solutions. A series of standard solutions of known hy- 

 drogen ion concentration must be prepared. The solutions as indi- 

 cated in Table I (page 501) are satisfactory for urine analysis. The 



1 Van Slyke and Palmer: Jour. Biol. Chem. 41, 567, 1920. 



2 Henderson and Palmer: Jour. Biol. Chem., 13, 393, 1913. 



