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 sufficient. As this method has not yet been applied to large quantities, the most suitable time has yet to be actually found.

Exact comparisons are only possible, when the test-tubes are of the same dimensions and have exactly the same thickness. For this purpose we must always arrange to have a sufficient stock of test-tubes answering perfectly to this requirement. In order to realize the importance of this proceeding, we only have to pour a slightly bluish solution into a wide and a narrow test-tube respectively, when we see that the former will show a much deeper blue colour than the latter. A faulty diagnosis would thus result.

The following cases are possible. The usual result of the reaction is either, dialysate of serum and of serum + organ negative, in which case no decomposition has taken place; and, if placenta had been used, we should assert that there was no placenta in the living state that had any connection with the particular organism; or else serum alone gives negative, and organ - serum positive, results. The diagnosis would indicate pregnancy, or, better still, the existence of a placenta that still stands in effective relations with the organism of the mother.

It may happen that the serum alone gives off substances to the dialysate, in sufficient quantity for the positive reaction to appear under the conditions