[This paper was read to a group of members of the Guild of St. Luke, St. Cosmas, and St. Damian in London in 1923, and was first published in The Catholic Medical Guardian, the quarterly journal of the Guild (Vol. II, No. 5, January, 1924). We are indebted to the Editor of that journal and to Father Vincent McNabb for permission to reprint the article. Its publication is timely in view of the declaration of a majority of the members of the Lambeth Conference to the effect that where the moral obligation of birth prevention exists, it is open to the parties concerned to employ any method to prevent conception, provided such method be in accord with Christian principles. Father Vincent McNabb's paper, written seven years ago, is an adequate answer to the Lambeth pronouncement.‐EDITOR.]