To the Editor:
—In conducting experiments with preserved complement, I have found that the complement apparently varies in strength from week to week, fluctuating from strong to weak and strong again, sometimes stronger the third week than the first.I have found this to be due to a factor, hitherto unnoted, namely, the marked variation in resistance of different batches of blood cells to hemolysis. I want, therefore, to issue this note of warning to all serologists utilizing my complement preservative (The Journal, Sept. 22, 1917, p. 973): It is necessary to retitrate the complement with each new supply of blood cells. For example, one batch of blood cells required 0.175 of complement to complete the hemolytic system. Another batch of cells, used two days later, required only 0.1. Still another batch of cells, used two days following the latter, required 0.125 of this same complement for the Wassermann tests.