On certain correction terms required in the equations for the kinetics of simple hœmolysis

The most satisfactory method hitherto available for the measurement of percentage hœmolysis has been the potassium cell method described in an earlier paper (Ponder and Yeager, 1930). This method, however, has certain limitations and disadvantages, two of which are particularly conspicuous. (i) The galvanometer which records the photoelectric current takes several seconds to deflect, and several seconds more to settle at zero. This determines that no more than four readings of the degree of hœmolysis can be made in a minute, and that only a few points can be obtained on the percentage hœmolysis curve for rapidly hœmolysing systems. Even these points, moreover, are apt to be inaccurate, for lysis is going on during the time taken for the galvanometer to move ; the degree of lysis recorded is thus always greater than that really present at the moment the photoelectric cell first receives the light. The effect is to move the percentage hœmolysis curve over to the right by a distance corresponding to about 0-05 minutes ; this shift is of little consequence if lysis is slow, but may introduce considerable error if it is rapid. (ii) The method is unreliable in the sense that its efficiency depends on factors which are controlled with difficulty and which are liable to vary. Photoelectric fatigue, although usually absent, may appear during any experiment, the voltage of the high tension battery or of the accumulator which supplies the lamp may vary, or the potassium cell may glow as a result of a careless exposure to the light in the interval before the cells are added to the lysin in the chamber. Experience shows that these accidents often happen, and the necessity of being continually on one’s guard against them makes the measurement of percentage hœmolysis much more difficult than would appear at first sight.