SECRETION. 455 



there is diminution in pregnancy by reason of deposition of phos- 

 phate within the i'oetal bones. 



THE SULPHURIC ACID is derived from the liberation and oxida- 

 tion of tissue sulphur. Sulphuric acid occurs in the urine in com- 

 bination with alkalies, principally sodium and potassium. The sul- 

 phur introduced into the system medically finds egress mainly in the 

 fasces, as it does not easily pass into the blood. From this it is 

 inferred that the sulphur eliminated is derived especially from the 

 transformation of the tissue-proteids. It runs parallel with urea 

 excretion. The daily quantity of sulphates excreted is 3 grams. 

 Proteid contains 1 per cent, of sulphur and 16 per cent, of nitrogen. 

 The aromatic or conjugated sulphates form one-tenth of the 

 total sulphates, and arise from bacterial putrefaction within the 

 intestinal canal, in intestinal obstruction, typhoid fever, etc. The 

 chief aromatic (ethereal) sulphates are phenol sulphate of potassium 

 and indoxyl sulphate of potassium. 



CARBONIC ACID in a state of combination is scarce in the urine 

 and only increases there after the use of alkaline carbonates and of 

 vegetable acids, which latter are transformed into carbonic acid by 

 oxidation. 



To sum up in an approximate average the very variable propor- 

 tions of the principal, normal constituents of the urine, it may be 

 said that with a mixed diet and moderate bodily movement there are 

 in every 100 cubic centimeters of daily urine: 



Water 96.00 grams. 



Solid components 4.00 " 



Urea 2.30 " 



Uric acid 0.03 " 



Sodium chloride 0.80 " 



Phosphoric acid 0.15 " 



Sulphuric acid 0.20 " 



Earthy phosphates 0.08 " 



Ammonia 0.04 " 



Fermentation of Urine. We have seen that the reaction of 

 urine is generally acid; but it can become alkaline, even in the 

 physiological state, from abundant ingestion of alkalies, or of salts 

 with organic acid. The intensity of the acid or alkaline reaction of 

 urine must necessarily vary, not only with the proportion of the 

 components that determine it, but also with the degree of dilution. 



The acidity of the urine may, however, be further increased by 

 a process of acid fermentation due to bacteria, in the presence, per- 

 haps, of vesical mucus. This fermentation may take place outside 



