Studies on Mammalian Red Cells 85 



lines. The initial part of the curve falls rather rapidly. It is possible 

 that in the normal system you also have a component in the blood 

 which cannot stand the hurly burly and vicissitudes of circulation and 

 breaks down very rapidly. This may explain the initial part of the 

 plateau. 



Another difficulty comes when you consider the bilirubin. Its 

 isotope concentration does not fall to zero between the initial peak and 

 the second peak. This is not in accord with the simple theory. The 

 situation is more complicated than the simple mathematical derivation 

 that we presented, but I don't believe that it is worth trying to improve 

 the theory without new and better data than is now available. 



The curves resulting from transfusion of red cells which Dr. Neuberger 

 showed you have always puzzled me. They shouldn't look that way. 

 As he pointed out, they show a negligible scatter, and we're almost sure, 

 not only from experimental work, but intuitively, that they shouldn't 

 be that way. They should have some sort of curvature at the beginning 

 and the end, and they don't have it. The interpretation of this type 

 of data may be more difficult than the interpretation of the ^^N data. 



Mollison: There is an apparent discrepancy between the results of 

 experiments with i^N and transfusion experiments. The experiments 

 with i5]s; suggest that a considerable proportion of red cells Uve for less 

 than the average life and that a considerable proportion live on for 

 many weeks after the average life. On the other hand, transfusion 

 experiments suggest that there is very little variation in life-span 

 between one red cell and another. Dornhorst* (1951) has pointed 

 out that the standard deviation of the life-span of red cells can be de- 

 duced from the number of transfused red cells surviving at the end of 

 the average life-span. When the number of cells surviving at different 

 intervals after transfusion is plotted, the points fall on a straight line, 

 and extrapolation of this line to the time axis gives an estimate of the 

 mean cell life. However, the curves often show a small tail at the end 

 so that a small proportion of red cells are still present at the end of the 

 mean cell life and it is this number which is related, mathematically, 

 to the standard deviation of the life-span. Personal observations suggest 

 that the standard deviation may be as small as 5 days. If this is true, 

 the ^^N curves relating to red cell life-span must be re-interpreted, as 

 Dr. Neuberger has said. 



*Dornhorst, A. C. (1931). Blood, to be published. "Interpretation of red 

 cell survival curves." 



