It must be understood that the circulation of the mother and of her child are each complete and self-contained. They come into relation in the double organ called the placenta, and it has been exhaustively proved that this organ is so constituted as in large measure to protect the child from injurious influences acting upon and in the mother. We may therefore speak of the placenta as a filter. Its protective action explains the facts, so familiar to medical men and philanthropic workers, that healthy and undamaged children are often born to mothers who are stricken with mortal disease--most notably, perhaps, in the case of consumption. It becomes a most important matter to ascertain the limits of the placental power, and by observation upon human beings and experiment upon the lower animals this matter has been very thoroughly elucidated of late years. There are many kinds of poison, and many varieties of those living poisons that we call microbes, which the placenta does not allow to pass through from the mother's blood-vessels into those of the child, and which are unable, fortunately for the child, to break down the placental resistance. On the other hand, there are certain microbes and certain poisons which readily pass through the placenta. Conspicuous amongst these are alcohol, lead and arsenic, and it is especially important to realize that alcohol injures the child not merely by its own passage through the placenta, but by injuring that organ, so that its efficiency as a filter is impaired. On the whole subject of expectant motherhood and the morbid influences which may act upon it, the greatest living authority is my friend and teacher, Dr. J. W. Ballantyne of Edinburgh. He contributed an important paper on this subject to our first National Conference on Infantile Mortality held in 1906.[22] I only wish it were possible to reproduce in full here Dr. Ballantyne's paper on the Ante-Natal Causes of Infantile Mortality. The unread critic who is so ready with the word fanatic whenever alcohol is attacked might begin to derive from it some faint idea of the quality and massiveness of the evidence upon which our case is based. Here it must suffice merely to quote the verdict at which Dr. Ballantyne arrives after surveying all the evidence on the subject that had been obtained up to the year 1906. He summarizes as follows:--