A subject of perennial interest is the origin of the infections which so often prove fatal after childbirth. At one time there was a universal impression that puerperal fever had its source in the patient. Then, as the result of an accumulation of evidence, there came the definite conclusion that the infectious material was usually introduced from without and was due either to the carelessness of the physician or of the midwife in attendance, or to some mistake by the nurse or by the patient herself. In this, as in most things in medicine, it seems not unlikely that the pendulum of opinion swung too far and that there is about to be differentiated a series of cases in which the origin of the infectious material will be found, as was formerly thought, within the patient's tissues.
One thing is very clear, micro-organisms of various kinds, under certain circumstances, may