AMOUNT AND COMPOSITION OF THE URINE 559 



rather difficult electrical or indicator method, the principle of which has 

 been described in Chapter V. Expressed in terms of C H , the acidity 

 varies between 4.7 x 10- 7 and 100 x 10~ 7 . The total potential acidity 

 that is, the number of H ions which will be formed in the face of a con- 

 tinual neutralization of those in solution may be obtained fairly accu- 

 rately by titrating the urine with Vio normal alkali in the presence of 

 neutral potassium oxalate, using phenolphthalein as an indicator (Folin). 

 The results may be expressed in acidity per cent in terms of c.c. N/10 

 NaOH required to neutralize 100 c.c. of urine. If the ammonia excretion 

 is added to the titration results, the total potential acidity is very closely 

 measured. In normal subjects the acidity is high in the relatively scanty 

 urine that is excreted during the night. In the forenoon more urine is 

 excreted and the acidity is much less, i. e., alkalinity much greater. This 

 alkaline tide in the forenoon is not dependent upon the accompanying 

 diuresis, and it is the only alkaline tide during the 24 hours. The old idea 

 of an alkaline tide following the ingestion of food is not correct. These 

 facts are taken advantage of in a test of renal efficiency in which the 

 conditions are standardized by having the patient, after awaking in the 

 morning, drink a definite volume of water, but take no food. The night 

 urine (from 11 p. M to 7 A. M.) and hourly specimens between 7 A. M. and 

 12 noon are collected and their volume and alkalinity (c.c. N/10 NaOH per 

 100 c.c.) measured. Typical results after drinking 500 c.c. water are 

 exhibited in the following table: 



(Adapted from Leathcs.) 



In this table, I represents the response of normal subjects in whom 

 diuresis and alkalinity both increased; II, that of nephritic patients in 

 whom the diuresis reaction was subnormal, but the alkalinity normal, 

 and III, more severe cases in whom both the diuresis and the alkalinity 

 were subnormal. 



Leathes has been able to show that this morning alkaline tide is de- 

 pendent upon a greater excitability of the respiratory center on waking 

 compared with that during the night. This causes pulmonary ventila- 

 tion to become more thorough during the morning hours than during 

 the night, so that more C0 2 is washed out of the blood, thus lowering its 

 acidity and causing alkali to be excreted by the kidney. The CO 2 content 



