CONTENTS XXlll 



9.2 Endogenous IVobilin Metabolism 554 



9.2.1 Enterohepatic Circulation 554 



9.2.2 Al)sorption from the Intestine 555 



9.2.3 Re-excretion of Urobilin by the Liver 555 



9.2.4 Physiological and Clinical Value of Estimation of 

 Total Urobilin Excretion 556 



9.2.5 Urobilin in Blood Plasma 557 



9.2.6 Urobilinuria 558 



9.3 Other End Products of Hemoglobin Catabolism 559 



9.3.1 Fecal Pigments 559 



9.3.2 Urinary Pigments 559 



9.3.3 Dipyrrolic Compounds 559 



10 Liberation of Hematin Iron and Fate of Globin . 561 



10.1 Introduction 561 



10.2 Excretion of Iron 562 



10.3 Nonhematin Iron in Tissues 562 



10.3.1 Bile Pigment Iron 562 



10.3.2 Transport Iron 563 



10.3.3 Storage Iron 565 



10.3.4 Estimation of Nonhematin and Hematin Iron. . . . 566 



10.3.5 Chemical Nature of Nonhematin Iron 567 



10.4 Fate of Globin 568 



11 Catabolism of Hematin Enzymes 568 



12 Distribution of Bile Pigments in Nature 569 



13 The Physiological Function of Bile Pigments 570 



XII. Hemoglobin Catabolism, II. Hematin and Porphyrins 573 



1 Introduction 573 



2 Metal)olism of Hematin 573 



2.1 Hematin and Methemali)umin in Blood Plasma 573 



2.2 Hematin in Blood Extravasations and in the Malarial Red 



Cell 574 



2.3 Metabolism of Hematin 575 



2.4 Toxicity of Hematin . 577 



3 Porphyrin Metabolism 577 



3.1 Introduction 577 



3.2 Endogenous Porphyrin Metabolism. 578 



3.2.1 Introduction 578 



3.2.2 Distribution of Porphyrins in the Human Body. . . 579 



3.2.3 Destruction of Porphyrins 582 



3.2.4 Conversions of One Porphyrin to Another 582 



3.2.5 Influence of Liver and Kidney on Urinary Porphyrin 

 Excretion 583 



3.2.6 Porphyrin Metabolism in Other Species 584 



3.3 Excretion of Porphyrins 586 



3.3.1 Introduction 586 



3.3.2 Excretion of Porphyrins of Isomeride Types I and III 586 



3.3.3 Porphyrins in Normal Excreta 588 



3.3.4 Porj)hyrins in Pathologic ?]xcreta 589 



3.3.5 Formation of Por[)hyrins by Bacterial Decomposi- 



' - tion of Hematin Compounds 592 



