580 THE CHEMISTRY OF THE URINE. 



It must not be supposed, however, that the post-prandial alkaline 

 tide is a universal phenomenon. It will be easily seen that the effect 

 of digestion upon the bases and acids of the blood must be somewhat 

 complex. The flow of alkaline saliva precedes, and that of bile and pan- 

 creatic juice rapidly follows, the gastric secretion ; and these, by removing 

 bases, tend to neutralise the effect of the removal of acid via the 

 stomach. From this cause, and from the increased proteid metabolism 

 induced by the food, it not infrequently happens that the urinary acidity 

 is from the first raised, instead of lowered, after a meal. 



According to Quincke, a periodic variation of acidity may occur dur- 

 ing the day, independently of food ingestion, 1 and in my experience this 

 is a more constant phenomenon. 



Gruber found that the urine may Become alkaline after a large con- 

 sumption of sodium chloride, and Eiidel 2 has recently stated that the 

 pure diuresis produced by such substances is in itself capable of inducing 

 this result. This may be true, under the somewhat extreme conditions 

 of experiment, but when the urinary constants are followed under 

 natural conditions from hour to hour, it is not found that the quantity 

 of urine passed during a given period has any regular influence on the 

 total acidity of the same period. 3 



Pathologically, a tendency to alkalinity is said to be found in most con- 

 ditions of debility, and especially in some types of anaemia ; probably from 

 diminished secretion of gastric juice, and from diminished general metabolism. 

 A process quite distinct from this occurs when, under the influence of 

 organisms (especially the Micrococcus urece), the urea and uric acid of the 

 urine are hydrolised into ammonium carbonate. In cystitis this may occur 

 in the bladder, and the urine is voided alkaline with ammonia. 



The acidity is especially high in scorbutic urine, and is increased to a greater 

 or less degree in some forms of dyspepsia, in diabetes, leukaemia, and in per- 

 nicious anaemia. 



THE NITROGENOUS COMPOUNDS. 



(a) Total nitrogen. The urinary nitrogen amounts, on an average, 

 to 15 grms. in the twenty-four hours. This comprises by far the greater 

 part of the nitrogenous loss to the body ; less than 1 grm. being eliminated 

 through the intestinal secretions and all other channels combined. 



Pathologically, the amount may be greatly increased ; 20 to 25 grms. 

 per diem is frequently observed in fever, and in severe forms of diabetes 

 50 grms. and upwards may be daily eliminated. On the other hand, a 

 marked diminution of the amount is seen in the condition of contracted 

 or granular kidney. 



Under normal conditions, the urinary nitrogen is distributed in 

 various compounds in the following proportions : About 86 per cent, of 

 the whole is found in the form of urea ; about 3 per cent, as ammonia, 

 3 per cent, as creatinin, 2 per cent, as uric acid and the allied xanthin 

 bases ; while the remaining 6 per cent, is present, in varying proportions, 

 in hippuric acid, in indol and skatol, in the urinary nucleo -albumin, 

 in the pigments, and in minute quantities of other constitutents. 



The total nitrogen is estimated by one of the many modifications of 

 Kjeldahl's process, which is founded on the fact that organic substances, 



1 Ztschr.f. Min. Med., Berlin, 1884, Bd. vii. Suppl. 22. 



2 Arch.f. exper. Path. u. Pharmakol., Leipzig, 1892, Bd. xxx. S. 41. 



3 Cf. Hausmann, Ztschr. f. klin. Med., Berlin, 1896, Bd. xxx. S. 362. 



