556 XI. HEMOGLOBIN CATABOLISM, I 



Watson {2989) found an average daily excretion by healthy men 

 of 180 mg. of urobilin, the values varying between 40 and 280 mg,, 

 usually between 100 and 200 mg. Assuming a total circulating hemo- 

 globin content of 825 g. (c/. Section 2.2.) and a lifetime of the red 

 cell of 120 days, about 250 mg. should be excreted per day, or to 

 judge from the bilirubin excretion, rather more. According to this 

 calculation, from to 85% (on the average 30%) of the urobilin is 

 destroyed, unless the corresponding amount of bilirubin is trans- 

 formed to substances other than urobilin. 



Figures similar to those of Watson can be calculated from the "hemolytic 

 index," i.e.y the amount of fecal urobilinogen excreted per day in mg. per 

 100 g. circulating hemoglobin. Heilmeyer and Oetzel {1219), Miller and 

 co-workers {194-9), and Singer {3566) found a hemolytic index of about 10-25. 

 Belonogowa {208) found the higher value of 30, but assumed a value for the 

 blood volume which is probably too low. Tlie hemolytic index is high in 

 pernicious anemia (oO-^SO) and in hemolytic jaundice (up to 800). Evidence 

 for the destruction of mesobilane in the liver has been found by Brule and 

 Garban {37S) and Felix and Moebus {743), but tetrahydromesobilane or 

 -bilene are probably more stable. Perhaps the loss of urobilin is mainly due 

 to the destruction of mesobilane and mesobilene. Baumgartel {194) found 

 that, in the presence of cysteine, liver reduction can lead to a complete 

 destruction of pyrrole rings. Urobilin may also be absorbed from the cir- 

 culating blood and destroyed in muscles and organs {cf. below). 



Small amounts of bilirubin remain vmaltered in the intestine {cf. above), 

 but the quantity is hardly large enough to account for the loss. Reconversion 

 of urobilin to bilirubin has been assumed repeatedly, without a shred of 

 evidence {37 0-37 2, 697, 29 H9). The chemical constitution of urobilin as now 

 known makes this assumption still less likely. On the basis of Whipple's 

 hypothesis of a pyrrole body complex {3044)^ it has been assumed that the 

 excretion of urobilin is proportional to the amount of hemoglobin destruction 

 only when the individual is in the state of blood balance {346,1-593,1984). 

 The later work of Whipple and co-workers has clearly shown that this assump- 

 tion is unjustified; even in a state of severe anemia the prosthetic group of 

 hemoglobin is quantitatively excreted as bile pigment {cf. Chapter XIII). 



The diet, particularly a meat diet, exerts an influence on urobilin excretion. 

 The smaller amount of urobilin in vegetarian feces is perhaps due to the less 

 complete conversion of bilirubin to urobilin {cf. above). 



9.2.4. Physiological and Clinical Value of Estimation of Total Urobilin 

 Excretion. The disappearance of a varying proportion of urobilin and the 

 possibility of incomplete conversion of bilirubin into urobilin introduce a 

 large margin of error into attempts to deduce the degree of hemoglobin 

 destruction from estimations of total urobilin excretion. The results of 

 Watson and Schwartz {2989, p. 'i.'AH) make one rather sceptical of the value 

 of the method for measuring the degree of hemoglobin breakdown in a single 

 case. In one instance 800 mg. pure /-tetraliydromesobilene, given per os 



