482 EXCRETION 



tion of the urinary creatinin is derived from the creatin of the meat 

 taken as food. But this is not its only source, for on a meat-free diet 

 and in starvation creatinin is still excreted. The absolute quantity in 

 the urine on a meat-free diet is constant for one and the same individual, 

 although different 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 creatinin is much greater 

 than on a protein-rich diet, as shown in the table on p. 477. So constant 

 is the quantity that a determination of the creatinin 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 amounts. Three are known with certainty dextrose, 

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

 acid (C 6 H 10 O 7 ), a body which can be derived from dextrose, is con- 

 stantly present in small amount as a conjugated acid, paired with 

 phenol or indoxyl. It gives Fehling's test, and thus may easily be 

 mistaken for sugar. Glycuronic acid becomes coupled very easily with 

 a large variety of substances, including many drugs, and care must be 

 taken after the administration of camphor, chloral hydrate, chloro- 

 form, nitrobenzol, etc., not to confound the largely increased excretion 

 of conjugate glycuronates in the urine with glycosuria. The yeast test 

 will turn out negative if the reduction is due to glycuronic acid, and 

 the polarimeter will show rotation to the right if it is due to dextrose. 

 The total quantity of carbo-hydrates, including glycuronic acid, 

 excreted in the urine of the twenty-four hours has been estimated at 

 2 to 3 grammes. The quantity of dextrose in normal human urine is 

 about 0-02 per cent., or about one-fifth of the proportion in blood. 



Proteins, mainly serum-albumin, are also found in normal urine in 

 minute quantities, on the average about 0-0036 per cent. (Morner). 



Pigments of Urine. The pigments of urine have not hitherto been 

 exhaustively studied ; but we already know that normal urine contains 

 several, and pathological urines probably additional, pigmentary sub- 

 stances. The best-known pigments in normal urine are urochrome, 

 the yellow substance which gives the liquid its ordinary colour; 

 uroerythrin, the pink pigment which often colours the deposits of urates 

 that separate even from healthy urine ; and urobilin, which, as has been 

 already stated, is identical with the faecal pigment stercobilin, and occurs 

 not only in many febrile conditions, but also in cases with no fever, such 

 as functional derangements of the liver, dyspepsia, chronic bronchitis, 

 and valvular diseases of the heart. The urobilin of urine represents, 

 mainly at least, the portion of the stercobilin which is not excreted with 

 the faeces, but absorbed from the intestine into the blood. The urobilin 

 in normal urine only exists in small amount in the fully-formed con- 

 dition, most of it being present as a chromogen or mother-substance 

 (urobi Imogen), which by oxidation, as on standing exposed to the air, 

 is converted into urobilin. On the addition of ammonia and zinc 

 chloride to a solution of urobilin a beautiful green fluorescence is 

 obtained, and the solution now shows an absorption band between 

 b and F. Urobilin and urochrome are related substances, bat the exact 

 nature of the relation has not been settled. There is some evidence 

 that a portion of the urobilin of urine is not derived from the intestine, 

 but manufactured probably in the liver. In hunger urobilin is still 

 excreted in the urine, although in greatly reduced amount. During 

 menstruation it is markedly increased, both in fasting and in normally 

 fed individuals. Urorosein is a red pigment which is produced from 

 its chromogen by the action of mineral acids e.g., strong hydrochloric 

 acid in the presence of an oxidizing agent, especially nitrites. 



