Experiments are recorded demonstrating the quantitative relations between cephalin, protein, and hydrochloric acid or calcium chloride in: (a) the precipitation of the cephalin-protein complex from serum; (b) the restoration of the coagulative (thrombin) activity of serum; (c) the acceleration of the coagulation of oxalated plasma; (d) the inhibition and reactivation of complement.

In all of these reactions an excess of cephalin or protein inhibited the reaction, whereas optimum activity occurred when the quantities of cephalin and ionized calcium or acid were present in amounts approximating their chemical equivalents. Under these conditions the inhibition of complement was complete and irreversible. With an excess of cephalin or protein, the inhibition of complement was reversible, complete activity being restored by the addition of an amount of calcium chloride approximating or moderately in excess of the chemical equivalent of the cephalin present.

Complement reversibly inactivated by cephalin was reactivated by ammonia-, zymin-, or heat-inactivated serum and also by the heated or unheated albumin but not by the euglobulin fraction of serum: the reactivation was associated with fractions containing the ionized calcium of serum.

Complement inactivated by both zymin and ammonia and then heated also reactivated the cephalin-treated complement. Conversely, both ammonia- and zymin-inactivated complement was reactivated by heated cephalin-inactivated complement. Neither cephalin nor calcium chloride was found effective in reactivating ammonia- or zymin-inactivated complement.

Removal of calcium from fresh serum, by preliminary precipitation of the euglobulins with carbon dioxide and subsequent dialysis of the albumin fraction with dilute acid, resulted in a diminution not only in the complement activity but also in the reactivating activity for cephalin-inactivated complement. Partial reactivation of both activities occurred on the addition of calcium chloride.

Finally, experiments are recorded demonstrating:

  1. That the complement and coagulative activity of plasma inactivated by treatment with magnesium hydroxide was reactivated by heated serum or the fractions thereof or by the addition of a definite concentration of hydrochloric acid;

  2. That the complementary activity of the prothrombin solutions prepared by adsorption of plasma with magnesium hydroxide and of the albumin and euglobulin fractions of serum bore no constant relation to their coagulative (prothrombin) activity;

  3. That these prothrombin solutions, prepared with magnesium hydroxide, like those prepared with tricalcium phosphate or by the saturation of plasma with sodium chloride, contained fibrinogen.

1

Presented at the meeting of the American Association of Immunologists at Toronto, Canada, March 28, 1934.

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