234 P. L. Mollison 



iron liberated from breaking-down red cells is not reutilized, 

 and so the disappearance of cells from the circulation 

 is accompanied by a disappearance of radioactivity. Such 

 experiments show that most red cells in the dog live for about 

 110 days; they also show that the standard deviation of life- 

 span is quite small — about 6 days (Brown and Eadie, 1953). 



When red cells are transfused from one normal subject to 

 another, a very different type of curve is found because the 

 blood then contains labelled red cells of all ages. Since red 

 cells live for rather more than 100 days, each day slightly less 

 than 1 per cent of the cells are expected to reach the end of 

 their life-span and leave the circulation. Transfusion experi- 

 ments lend solid support to the idea that red cells have a 

 definite life-span which, in man, is about 110-120 days. 



Dornhorst (1950) has aptly compared the red cell to the 

 V-l pilotless bomb, starting on its journey with a definite load 

 of fuel and crashing precipitously to earth when the fuel is 

 exhausted. 



At one time it was suggested that red cells were slowly 

 battered to pieces in the circulation (Rous and Robertson, 

 1917). However, this view is more in keeping with the idea 

 that red cells are inanimate particles rather than that they 

 are actively metabolizing cells. There is some direct evidence 

 against the idea that cells are battered to pieces after a finite 

 number of collisions in the circulation. For example, if red 

 cells are transfused to a patient with double the normal 

 cardiac output so that they travel faster and further than 

 normal red cells, they survive for the same time as in a normal 

 circulation (unpublished observations). 



In fact, it appears that red cells are capable of a limited 

 amount of self-repair; for example, they can synthesize 

 phospholipids and thus replace lipids lost from their surface 

 (Altman, 1953). It is of some interest that red cells which 

 have been washed a dozen or more times in normal saline, and 

 have presumably lost some cell lipids, survive normally after 

 re-injection into the circulation (Hughes Jones and Mollison, 

 1956). 



