442 



A MANUAL OF PHYSIOLOGY 



arises in the metabolism of the tissues probably from the decom- 

 position of uric acid. It is known that outside of the body uric acid 

 may be made to yield oxalic acid. Calcium oxalate crystals are 

 often seen in urinary sediments. 



Kreatinin (C 4 H 7 N S O). Kreatinin is the anhydride of kreatin 

 (Fig. 1 66). Its formula differs from that of kreatin only in possess- 

 ing the elements of one molecule of water less ; and kreatinin can be 

 obtained by boiling kreatin with dilute sulphuric acid, then neu- 

 tralizing with barium carbonate, filtering, evaporating the nitrate to 

 dryness on the water-bath, and 'extracting the residue with alcohol. 

 From its alcoholic solution it crystallizes in colourless prisms 

 Kreatinin forms crystalline compounds with various acids and salts. 

 One of the best known of these is kreatinin-zinc-chloride, formed 

 on the addition of zinc chloride to an alcoholic or watery solution 

 of kreatinin, often in the shape of beautiful thick-set rosettes of 

 needles (Fig. 167). A portion of the urinary kreatinin is derived 

 from the kreatin of the meat taken as food. But this is not its only 

 source, for on a meat-free 

 diet and in starvation krea- 

 tinin is still excreted. The 

 absolute quantity in the urine 

 on a meat-free diet is con- 

 stant for one and the same "J 

 individual, although different ? 



FIG. 166. KREATIN. 



FIG. 167. KREATININ-ZINC-CHLORIDE. 



in different persons, and independent of the total amount of nitrogen 

 eliminated. Hence on a diet poor in protein the percentage of the 

 total nitrogen excreted as kreatinin is much greater than on a protein - 

 rich diet, as shown in the table on p. 437 . So constant is the quantity 

 that a determination of the kreatinin may be used as a check upon 

 the complete collection of the urine. 



Carbo-hydrates are normally present in human urine, but only in 

 very small amount. Three are known with certainty dextrose, 

 isomaltose, and the so-called animal gum or urine dextrin. Glycu- 

 ronic acid (C G H 10 O 7 ), a body which can be derived from dextrose, 

 and which occurs in the urine in increased amount after the adminis- 

 tration of chloroform, chloral, nitrobenzol, camphor, and other 



least frequently present in 

 "., indoxyl or skatoxyl, as 

 and thus may easily be 

 mistaken for sugar. The total quantity of carbo-hydrates, including 

 ^lycuronic acid, excreted in the urine of the twenty -four hours has 

 )een estimated at 2 to 3 grammes. The quantity of dextrose in 



