1. Under certain conditions, mechanical agitation destroys the complementary activity of guinea pig serum. It is most injurious when carried out constantly at a temperature of 37° C., but it is extremely insignificant at 10° C. After the first few hours at 37° C., the destruction of complement proceeded much more rapidly, and after six hours it was almost complete. On the other hand, within one hour shaking had almost no destructive effect on complement, even at 37° C. From this we may conclude that the several shakings which are necessary for fixation experiments during incubation do not modify perceptibly the outcome of the reactions.

2. The rate of destruction of the complement of guinea pig serum at temperatures above 45° C. is progressively greater as it approaches 55° C., at which temperature the activity is reduced in thirty minutes to one-thirtieth to one-fortieth of the original strength of the unheated serum; but it is not completely destroyed, as is commonly assumed.

The velocity of destruction of guinea pig complement when exposed to 55° C. for various lengths of time is found to be quite irregular, and not proportional to the length of time. This irregularity, however, presents a certain rhythm, a period of greater destruction alternating with one of less destruction.

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