=3. Perception of active and passive movements of the fetus= is accepted as a third incontrovertible sign of pregnancy. There is some difference of opinion concerning the value of “quickening” alone as a positive sign of pregnancy. But if the fetal movements are also perceptible by the obstetrician through the mother’s abdominal wall or by vaginal examination, there can be no doubt about the diagnosis. The movements felt by placing the hand upon the abdomen are termed _active movements_, while the _passive movements_ result from internal or external _ballottement_. Ballottement is accomplished by giving a sharp or sudden push to the head or an extremity, and feeling it rebound in a few seconds to its original position. Passive movements may be felt early in the fourth month, and active movements after the 18th or 20th week. PHYSIOLOGY OF PREGNANCY A general understanding of the physiology of pregnancy is indispensable to an appreciation of the importance of observing the present-day teachings about the hygiene of pregnancy. Upon this, in turn, must rest intelligently administered prenatal care, one of the most important branches of obstetrics. The physiology of pregnancy really represents an adjustment of the various functions of the maternal organism, which are altered to meet the demands made upon the mother’s organs by the body which is developing, growing and functioning within hers. These adjustments are in the nature of an emergency service, since they come into existence and operate only while needed, which is during pregnancy, and promptly disappear when the need for them ceases with the birth of the child. The mother’s body then begins to return to its normal, non-pregnant state, which, with the exception of the breasts, which function for nine or ten months, is accomplished in a few weeks. But in addition to the normal changes in physiology in the course of pregnancy, there are frequently abnormal changes, too, which may be symptoms of grave complications. The detection of these symptoms, and the employment of treatment which they indicate, constitute one of the most valuable aspects of prenatal care. Although, as might be expected, the alterations in the structure and functions of the maternal organism are most marked in the generative organs, there are definite changes in other and remote parts of the body as well. And there are adjustments in metabolism, which, though not wholly understood, are now widely recognized as important. It is pretty generally believed that as a direct, result of pregnancy, certain substances are created, possibly by the corpus luteum, which circulate in the blood and definitely influence the maternal functions. It is possible that a development of the present imperfect knowledge of these substances will result ultimately in the discovery of a blood reaction which will serve to diagnose pregnancy in an early stage.