Weltmann1 found that when normal serum is heated in a boiling water bath, coagulation occurs after a few minutes, and diffuse turbidity develops. If, however, the serum has been diluted 1: 50 with distilled water, coagulation takes place only if certain electrolyte solutions are added. Then flocculation, as well as turbidity, occurs. Within a certain range the intensity of this coagulation is directly proportional to the nature and concentration of the electrolyte.2
Weltmann1 found also that when normal serum is diluted 1: 50 with differently concentrated solutions of calcium chloride in distilled water, different intensities of turbidity and flocculation occur after fifteen minutes of heating. He also demonstrated that the concentrations of calcium chloride at which turbidity and flocculation first appear are constant, provided normal serums have been used. Since a beginning flocculation may be distinguished more easily than a slight turbidity, only the flocculation values are