LIFE SPAN OF THE ERYTHROCYTE 511 



glycine in which one third of the nitrogen was present as this isotope. 

 Maximum isotope concentration in the hemin was reached in thirty 

 days after the glycine was fed. This remained constant for many 

 weeks and then declined rapidly. In this experiment there was 

 certainly a minimum of interference with normal metabolism. 



Fundamental to the deduction of the life of the cell from the excre- 

 tion of bilirubin or urobilinogen, or from the rate of disappearance of 

 cells containing sulfhemoglobin, is the assumption that breakdown 

 products of the iron-free prosthetic group are not used in the syn- 

 thesis of new hemoglobin. The work of Whipple and his collaborators, 

 discussed in Chapter XIII, fully justifies this assumption. Although 

 radioactive iron has been used by Hahn (1087,1092,1095) and his 

 collaborators for the study of hemoglobin formation, it could not be 

 used for the determination of the life of the cell, since iron liberated 

 by hemoglobin breakdown is used again for the synthesis of new 

 hemoglobin (Cruz, Hahn, and Bale, 515; cf. also Chapter XIII). 



The data we have so far discussed refer to the nonnucleated erythrocytes 

 of mammals. Hevesy and Ottesen {1265) have used the fact that nucleo- 

 protein is present in avian corpuscles to determine the life of these in the 

 hen by means of radioactive phosphorus. No exchange reactions were 

 observed between the nucleic acid of corpuscles and sodium phosphate, so 

 they assume that the radioactive phosphorus enters the cell during its 

 synthesis. Radioactive phosphate was fed in amounts sufficient to keep its 

 concentration in the plasma at a constant level. They measured the time 

 taken for the desoxyribose nucleic acid to reach a constant level of radio- 

 activity, and found a linear increase from the 5th to the 33d day after the 

 commencement of feeding, giving a lifetime of 28 days for the cell. It is 

 unlikely that the normal synthesis or breakdown is interfered with by the 

 labelled phosphate, and one must therefore assume that the length of life 

 of erythrocytes in the hen is of a different order from that found in dog or 

 man.* 



2.3. Life Span of the Cell Deduced from Histological 

 and Immunological Evidence 



Here again, two quite different types of experiment have given reasonable 

 concordance in their results. One approach has been the deduction of the 

 life span of the red cell from the maturation time of reticulocytes. Heilmeyer 

 {1206) found a maturation time for the reticulocyte of 24 hours, in agree- 

 ment with earlier workers {554,2449,2537). If the erythrocytes leave the 



* This has meanwhile been confirmed (Hevesy, 1262b). Shemin, London, and 

 Rittenberg (2o42a) have recently found, however, that the mature avian erythrocyte 

 continues to synthesize hemoglobin. The problem in this phylum is thus quite different 

 from that in mammals. 



