ALKALINE AND EARTHY PHOSPHATES. 365 



integrating tissues probably consisting not of urea, but of cre- 

 atin and creatinin, which subsequently are partly resolved into 

 urea, partly discharged, without change, in the urine. The 

 names of some other substances of which there are commonly 

 traces in the urine, will be found in Table II, p. 358. It has 

 been shown by Scherer that much of the substance classed as 

 extractive matter of the urine, is the peculiar coloring matter, 

 probably derived from the haemoglobin of the blood. 



Saline Matter. The sulphuric acid in the urine is combined 

 chiefly or entirely with soda and potash : 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, pro- 

 duced by the changes that take place in the burning. Dr. 

 Parkes, indeed, considers that only about one-third of the sul- 

 phuric acid found in the urine is derived directly from the 

 food. 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 nitro- 

 genous tissues, the other elements of which are resolved into 

 urea and uric acid. It may be in part derived also, as Dr. 

 Parkes observes, 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 generated during combination with the sulphur, 

 is one of the subordinate means by which the animal tempera- 

 ture is maintained. 



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

 in the urine, uncombined with oxygen ; for after all the sul- 

 phates have been removed from urine, sulphuric acid may be 

 formed by drying and burning it with nitre. Mr. Ronalds 

 believes that from three to five grains of sulphur are thus 

 daily excreted. The combination in which it exists is certain : 

 possibly it is in some compound analogous to cystin or cystic 

 oxide (p. 367). 



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 the former as with the latter. In 

 blood, saliva, and other alkaline fluids of the body, phosphates 

 exist in the form of alkaline or neutral acid salts. In the 

 urine they are acid salts, viz., the phosphates of sodium, am- 

 monium, calcium, and magnesium, the excess of acid being, 

 according to Liebig, due to the appropriation of the alkali 



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