6 3 2 THE CHEMISTRY OF THE URINE. 
sulphur" of the sulphates. 1 We have but little knowledge of the actual 
forms in which this neutral sulphur is excreted. As one source of the 
unoxidised sulphur compounds, we may look to the taurin of the bile, 
since it lias been shown (in the dog) that when the bile is diverted 
from the bowel by means of a fistula, the neutral sulphur of the urine is 
diminished ; experimental or pathological blocking of the bile duct, on 
the other hand, increases it. 2 A second portion is probably present in 
a compound or compounds analogous to cystine, 3 and in actual cystinuria 
the neutral sulphur is, of course, greatly increased (cf. p. 603). 
Minute quantities of sulphocyanides are always present, probably 
owing to reabsorption from the saliva which is swallowed, and these 
contribute to the " neutral " sulphur. 4 But none of the sources we 
have mentioned will account for the whole of the unoxidised sulphur 
present, which must partly exist in compounds of which we have no 
knowledge. 
To estimate the neutral sulphur, a small quantity of the urine is evaporated, 
and the residue fused with alkaline carbonates and nitrate of potassium. By 
this means the whole of the sulphur present is oxidised to sulphates, and these 
are estimated as barium sulphate. A separate estimation of the sulphuric acid 
originally present is made, and the amount deducted from the figure obtained, 
as above. The excess is a measure of the neutral sulphur, in terms of sulphuric 
acid. 
Phosphoric acid. — The greater part of the phosphates of the 
urine is derived directly from those ingested with the food, but a small 
proportion arises from the oxidation of the nuclein, lecithin, and 
protagon of the tissues. The phosphates are increased by animal food, 
especially when this is rich in nucleo-proteids (Weintraud), and are 
diminished by vegetable diet. The phosphoric acid of plants is mostly 
present as insoluble earthy phosphates, which are not absorbed. On 
this account the urine of herbivora is notably poor in phosphates. In 
man the quantity is necessarily very variable, and ranges from 1 to 
8 grms. of phosphoric acid in the urine of twenty-four hours ; it com- 
monly amounts to about 3 '5 grms. 
The nature of the salts present has been fully discussed in the 
section devoted to the chemical reaction of the urine. Part of the 
phosphoric acid is present in combination with linie and magnesia, but 
a greater part is combined with the alkalies. Some importance has 
been attached to a change in the relative proportion of the " earthy " 
and "alkaline" phosphates in diseased conditions, the estimation being- 
made by adding ammonia to the urine and so precipitating the former. 
But the information so obtained may be misleading, as whatever the 
form of calcium or magnesium salt originally present in the urine (e.g. 
sulphates or chlorides), a precipitate produced by ammonia would contain 
these bases as phosphates, since an interchange of acids would take 
place with the alkaline phosphates. From alkaline urines magnesium 
ammonium phosphate (triple-phosphate) frequently separates in char- 
acteristic crystals ; and in the deposit from feebly acid specimens 
1 Salkowski, VireJtow's Archiv, 1875, Bd. lviii. S. 472. 
- Cf. Kunkel, Areh.f. d. ges. Physiol., Bonn, 1877, Bd. xiv. S. 344. 
3 Goldmann and Banmann, Ztschr. f. physiol. Chan., Strassburg, 1888. Bd. xii. 
S. 254. 
4 Leared, Proc. Poy. Soc. London, 1870, vol. xvi. p. 18 ; I. Munk, Virchow's Archiv, 
1877, Bd. lxix. S. 354. 
