found wanting in this branch of practical application, then it is quite certain that he has not mastered the method, and no special investigations should be undertaken without such a certificate of capacity. No conscientious student should make use of a particular method without having made sure, by some means or another, that he is master of it; and the diagnosis of pregnancy supplies these means.
A further important rule is, that we must never allow current theories to mislead us. The assumption of a specific action of the defensive ferments has been established on the strength of the facts derived from experiments, but it has still to be supported by means of exhaustive investigations. Nor should any final conclusion ever be expressed in regard to a particular case, until it has been definitely determined by clinical means. It is in this respect that pregnancy offers such a sure basis. we do not know of any other condition which allows of such a clear and indubitable estimate of method. It either exists or it does not, and is never open to a discussion of "probabilities."
Valuable service is rendered to research as a whole, if every case, which gives an unexpected result in respect of its reaction, is thoroughly investigated. In the first place the dialysation tubes should be changed, or else another organ should be used. If the result always recurs, we still have to exclude the
