CH. XII.] REACTION. 273 



give us valuable information as to the relative activities 

 of the two organs. 



A of blood is about 0-55 C., the same as that of a 0*9 

 per cent, solution of sodium chloride. 



A of urine varies considerably with the diet, volume of 

 fluid taken and other conditions. For the mixed 24 hours 

 urine of an average man it is usually about 1-2 C. The 

 following values are of interest in this connection : 



A x volume of urine = molecular diuresis. 



is of considerable pathological signi- 



NaCl per cent. 



ficance. It is fairly constant in health, varying between 

 1*25 and 1-6. It exceeds 1-7 in heart disease or in any 

 condition that causes a retardation of the renal circulation. 

 The only febrile condition in which it is less than 1-7 is 

 malaria. 



IV. Reaction. 



Normal human urine is generally acid to litmus, the 

 average P H of 24 hour specimens being about 6-0. The 

 reaction varies with the diet, being greatest on a meat diet, 

 owing to the oxidation (in the body) of the sulphur and 

 phosphorus to sulphuric and phosphoric acids. On a 

 vegetable diet, however, the urine may become alkaline, 

 as it is in herbivora, owing to the organic salts being 

 oxidised to alkaline carbonates. During the secretion of 

 the acid gastric juice into the stomach, the urine may 

 become alkaline, the so-called " alkaline tide." 



The acid reaction of the urine is mainly due to the 

 excretion of acid phosphates and of weak organic acids. A 

 certain amount of the acids produced in the body are 

 neutralised by ammonia and excreted as ammonium salts 

 in the urine. The ingestion of acids or of acid phosphates 

 usually leads to an increase in the excretion of titratable 

 acids (or acid salts) and of non-titratable neutral am- 



