Use of a Logistic Function in Expressing Kinetic Hemolysis Data

A method of rectifying sigmoidal kinetic hemolysis curves is described. The curves are described, within limits, by the equation t = K(l/1 - l)(1/n) where t is time, K is a constant, l expresses the degree of lysis, and l/1 - l is the ratio of lysed to unlysed cells. This description holds over a wide range of red cell and lysin concentrations, provided the conditions are not substrate limited and the lysin preparation is reasonably stable. Graphical solution of the logarithmic transformation of the equation yields straight lines, and the intercepts of these lines with time ordinates may be used to define a time of initial lysis or, under suitable conditions, a time of 50% lysis. The time of initial lysis is inversely related to the lysin concentration, and thus its reciprocal may be used to precisely define units of lytic activity.