Decrees of the Catholic Church are cited in these pages, not because morality is an asset of the Catholic Church alone, but because it alone pronounces officially on these medical subjects after careful consideration by competent specialists. This Church has made decisions in comparatively few medico-moral cases, and the questions still undecided authoritatively are very numerous. They are quite difficult, too, because judgment supposes a knowledge of both medicine and ethics, a combination seldom found in one person. As physicians do not know ethics, and moralists do not know medicine, there is often trouble in getting at even a statement of the questions at issue between them. In the preface to _Essays in Pastoral Medicine_, in 1906, I mentioned a noted case of this kind, and in 1911 a similar incident occurred in a discussion of the morality involved in the sterilization of criminals and the defective by the state. This dispute was taken up by the leading canonists and moral theologians in the United States, Belgium, Holland, Austria, Spain, Italy and France, and for nearly two years these men wrote article after article based upon utterly erroneous physical data. The books we have on medico-moral subjects are either obsolete at present, or insufficient; or, more commonly, they are the work of amateurs in medicine. These last are worthless when they are not harmful. If, however, I may judge from the questions sent to me for answer by clergymen and physicians from all parts of the country, our theological seminaries and medical schools are in grave need of courses on the morality of medical practice. In this book, to the preparation of which I have given years of anxious thought because of the extreme responsibility involved in its decisions, the data for the most important parts of such courses are presented. AUSTIN O'MALLEY. THE ETHICS OF MEDICAL HOMICIDE AND MUTILATION THE ETHICS OF MEDICAL HOMICIDE AND MUTILATION CHAPTER I GENERAL PRINCIPLES CONCERNING SUICIDE AND HOMICIDE