A Comparison of the Von Krogh Formula (Logistic Function) and the Method of Probits As Applied to Hemolysis by Complement

Abstract

The von Krogh formula (logistic function) relating hemolysis, y, to amount, x, of complement, C′, describes a symmetrical distribution curve of red cell susceptibility to lysis when differentiated with respect to log x. This curve is almost identical with the normal distribution curve, to which hemolysis by C′ has been related by the use of the method of probits. The latter curve, being more completely understood theoretically and statistically, should be used in preference to the former. Erroneous applications of the logistic formula are discussed.