THE KIDNEYS AND URINE. 363 



Extractives. Besides mucus and coloring matter, urine contains a 

 considerable quantity of nitrogenous compounds, usually described under 

 the generic name of extractives. Of these, the chief are: (1) Kreatinin. 

 (C 4 H 7 N 3 O) a substance derived, probably, from the metamorphosis of mus- 

 cular tissue, crystallizing in colorless oblique rhombic prisms; a fairly 

 definite amount of this substance, about 15 grains (1 grm.), appears in 

 the urine daily, so that it must be looked upon as a normal constituent; it 

 is increased on an increase of the nitrogenous constituents of the food; 

 (2) Xanthin (C 6 N 4 H 4 2 ), an amorphous powder soluble in hot water; (3) 

 Hypo-zanthin, or sarkin (C B N 4 H 4 0); (4) Oxaluric acid (C 3 H 4 N 2 4 ), in 

 combination with ammonium; (5) Allantoin (C 4 H 6 N 2 3 ), in the urine 

 of the new-born child. All these extractives are chiefly interesting as 

 being closely connected with urea, and mostly yielding that substance on 

 oxidation. Leucin and tyrosin can scarcely be looked upon as normal 

 constituents of urine. 



Saline Matter. The sulphuric acid in the urine is combined chiefly 

 or entirely with sodium or potassium; forming salts which are taken in 

 very small quantity with the food, and are scarcely found in other fluids 

 or tissues of the body; for the sulphates commonly enumerated among 

 the constituents of the ashes of the tissues and fluids are for the most 

 part, or entirely, produced by the changes that take place in the burn- 

 ing. Only about one-third of the sulphuric acid found in the urine is 

 derived directly from the food (Parkes). Hence the greater part of the 

 sulphuric acid which the sulphates in the urine contain, must be formed 

 in the blood, or in the act of secretion of urine; the sulphur of which the 

 acid is formed being probably derived from the decomposing nitrogenous 

 tissues, the other elements of which are resolved into urea and uric acid. 

 It may be in part derived also from the sulphur-holding taurin and 

 cystin, which can be found in the liver, lungs, and other parts of the 

 body, but not generally in the excretions; and which, therefore, must be 

 broken up. The oxygen is supplied through the lungs, and the heat gen- 

 erated during combination with the sulphur, is one of the subordinate 

 means by which the animal temperature is maintained. 



Besides the sulphur in these salts, some also appears to be in the urine, 

 uncombined with oxygen; for after all the sulphates have been re- 

 moved from urine, sulphuric acid may be formed by drying and burning 

 it with nitre. From three to five grains of sulphur are thus daily ex- 

 creted. The combination in which it exists is uncertain: possibly it is in 

 some compound analogous to cystin or cystic oxide (p. 365). Sulphuric 

 acid also exists normally in the urine in combination with phenol 

 (C 6 H 6 O) as phenol sulphuric acid or its corresponding salts, with 

 sodium, etc. 



The phosphoric acid in the urine is combined partly with the alkalies, 

 partly with the alkaline earths about four or five times as much with 



