Estimation of the Life Span of Red Blood Cells

A modified method for fitting the model of Shemin and Rittenberg to study the life span of red cells is described. In this modification the assumption that incorporation of tag is complete before any cells die is relaxed. A recursion formula useful for fitting the model on the digital computer is given. Good results were obtained with data from the sheep, rat, cat, rabbit, and the dog, whereas in several of these cases the method of Shemin and Rittenberg was not satisfactory. By varying critical parameters of the model a continuum of curves is possible. Curves which formerly were explained on the basis of random death can be obtained without this assumption. Limitations and implications of the method are discussed.