562 XI. HEMOGLOBIN CATABOLISM, I 



These researches have shown that iron of broken-down hemo- 

 globin is carefully husbanded and used for synthesis of fresh hemo- 

 globin, that both the absorption of iron from the gastrointestinal 

 tract and its excretion are slow, and that the former is more readily 

 adjusted to the needs of the organism than the latter. The absorp- 

 tion of iron and its incorporation in the hemoglobin molecule will be 

 discussed in Chapter XIII. 



10.2. Excretion of Iron 



Contrary to earlier assumptions, Widdowson and McCance {1797,1798, 

 3070) found by careful studies of the iron balance that of injected iron little 

 was excreted in urine and none in feces, and also that excretion was not 

 raised after large doses of iron had led to its accumulation in the body. 

 Lintzel ilo7S), who reviewed the earlier literature, had also found only a 

 small fecal excretion of iron in men (less than 0.9 mg. per day). These 

 results were confirmed and extended by experiments of Hahn, Whipple, and 

 co-workers with radioactive iron, F" {1092,1093,1191), and of Copp and 

 Greenberg {Jt89) with Fe« {cf. Chapter XIII, Section 4.2.3.). The dog ex- 

 cretes 0.05-0.4 mg. of its body iron per day in the feces, showing no influ- 

 ence by feeding and little by injection of iron. Normally only 0.01 mg. iron 

 was excreted in the bile. After increased hemoglobin destruction, e.g., by 

 phenylhydrazine, this rose to 0.1-1.0 mg. per day. The increase was pro- 

 portional to tlie increase of bilirubin excretion, but represented only 3% of 

 the hemoglobin which underwent destruction. The remainder was stored, 

 even when excess iron was available in the body. Similarly only a small 

 fraction (2-8%) of radioactive iron was excreted in feces and urine for a 

 few days after intravenous injection {1093) and the excretion in the bile 

 was also little increased {10If7). Little or none was excreted in the urine 

 {1093,925,926) in the rat. Only a small and variable percentage of Fe" is 

 excreted in bile, feces, and urine. 



10.3. Nonhematin Iron in Tissues 



10.3.1. Bile Pigment Iron. Probably all the iron entering the iron 

 stores via catabolic processes passes through the bile pigment iron 

 stage. While the catabolism of hemoglobin provides the greatest 

 part of the iron liberated by catabolic processes, it is uncertain how 

 much of the total bile pigment iron in the body (if this could be 

 determined at any one moment) is actually derived from hemoglobin, 

 since some compounds containing bile pigment iron, e.g., inactivated 

 catalase, seem much more stable than choleglobin. 



Within the erythrocyte, however, the nonhemoglobin hematin 

 compounds may be neglected, and the bile pigment iron may be con- 

 sidered as solely deriving from hemoglobin. The high concentration 



