510 XI. HEMOGLOBIN CATABOLISM, I 



formation had been given. A mean value of 124 days was obtained 

 on four dogs. This gives a value for the normal daily bilirubin excre- 

 tion of 83 mg. The value actually found by Whipple during control 

 periods on the same dogs was 85 mgs. As Hawkins and Whipple 

 point out: first, it is unlikely that this agreement is fortuitous; and 

 second, the contribution made to the normal daily excretion of bili- 

 rubin by myohemoglobin seems to be slight (c/. Section 9.3.3.). 

 Similar values (94-117 days) were obtained by Harne and collab- 

 orators {1130) by measuring the time between the first and second 

 reticulocyte shower in monkeys. 



2.2.2. Urobilin Excretion. Measurement of the excretion of urobilinogen 

 in feces and urine has the advantage that it can be carried out on normal 

 individuals. There is, however, little doubt that the values for urobilinogen 

 excretion are lower than those for bilirubin excretion; bilirubin is either not 

 quantitatively converted into urobilinogen, or the latter is destroyed in the 

 body. The figures obtained for the average life of the human erythrocyte 

 by measurement of urobilinogen excretion are, therefore, too high. A number 

 of workers have used the urobilinogen excretion to measure hemoglobin 

 turnover {208J219J736M09,'2110,2112.259Jt,2987;cf. also 1949,2566). Large 

 variations of daily urobilinogen excretion have been found by one and the 

 same worker. Thus Watson {2987) found values of 40-280 mg. per day; 

 these are probably at least in part due to the irregularities of fecal excretion. 

 The values of Heilmeyer and Oetzel {1219) and Watson {2987) give a life 

 span varying from 160-300 days with an average somewhat above '200 days; 

 the values of other workers fall mostly into the same range. The values are 

 probably .still 25% too high owing to losses in the urobilinogen estimation 

 (Watson, 2984^)- If this is taken into account, it will he seen that tlie lowest 

 values agree with those deduced bj^ other methods for the average lifetime 

 of the red cell. 



2.2.3. Other Methods. Two quite different methods, based on 

 pigment metabolism, have given results for man which agree with 

 the data of Hawkins and W'hipple for the dog. The slow disappear- 

 ance of sulfhpmoglobin from the circulating blood has been known 

 for some time. The erythrocyte is unable to reconvert sulfhemo- 

 globin into hemoglobin {cf. Chapter XH). Jope {14-27) measured the 

 rate of disappearance of sulfhemoglobin over four months and found 

 complete disappearance of sulfhemoglobin-containing cells in about 

 114 days. These cells have therefore the same lifetime as normal 

 erythrocytes. A lifetime of the hematin, and therefore of the ery- 

 throcyte, of about 127 days was obtained by Shemin and Rittenberg 

 (2543) by measuring the excess of the N^^ isotope in hemin prepared 

 from blood, at various periods after one of these workers had ingested 



