EXCRETION 443 



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, pig- 

 mentary substances. 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, sometimes termed normal urobilin, to distinguish it from 

 the so-called febrile 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. Normal and febrile urobilin are 

 saidjto show F cert ainfspectroscopic differences, ' but are nevertheless 

 one and the same substance, and represent,^ mainly at' least, the 



FIG. 168. PEPSIN IN URINE. DIASTATIC FERMENT IN URINE. 

 AT DIFFERENT TIMES OF THE DAY (HOFFMANN). 



portion of the stercobilin which is not excreted with the fasces, but 

 absorbed from the intestine into the blood. The urobilin in normal 

 urine only exists in small amount in the fully-formed condition, 

 most of it being present as a chromogen or mother-substance (uro- 

 bilinogen), 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, but 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 pro- 

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

 hydrochloric acid especially in the presence of an oxidizing agent. 



The pigments of the blood and bile and some of their derivatives 

 are of common occurrence in the urine in disease. Hcsmatoporphyrin 

 has not only been found in some pathological conditions, but is 



