460 THE UEIXE. 



some of this ill-defined substance consists of Creatin and 

 Creatinin, two crystallizable substances derived, probably, 

 from the metamorphosis of muscular tissue. These sub- 

 stances appear to be intermediate between the proper 

 elements of the muscles, and, perhaps, of other azotized 

 tissues and urea : the first products of the disintegrating 

 tissues probably consisting not of urea, but of Creatin 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. 451. It has been shown by Scherer that much of the 

 substance classed as extractive matter of the urine, is the 

 peculiar colouring matter, probably derived from the 

 hrcmo-globin of the blood. 



Saline Matter. The sulphuric acid in the urine is com- 

 bined 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, produced by the changes that 

 take place in the burning. Dr. Parkes, indeed, considers 

 that only about one-third of the sulphuric 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 

 nitrogenous tissues, the other elements of which are re- 

 solved into urea and uric acid. It may be in part derived 

 also, as Dr. Parkes observes, from the sulphur-holding 

 taurin and cystin Avhich 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 gene- 



