In order to carry out the particular procedures of diagnosis and treatment which belong within the province of the social worker, a certain amount of medical knowledge is needed. Because this is true, it has often been assumed that the social worker must be a trained nurse, prepared by months or years of experience in a hospital. But experience has shown that much of the knowledge possessed by nurses who have had this training cannot be used by the home visitor. On the other hand, the information which the social worker needs is often quite lacking even in well-trained nurses. Furthermore, it may be said with truth that the training of a nurse, as we know it in America at any rate, really unfits a woman in some respects for the work of a social worker, since it accustoms her to habitual obedience and subordination. These habits are very useful in their proper place, but they are antagonistic upon the whole to the temper and mental activity which is important in the social worker. I mean the temper of aggression in relation to disease, and the mental attitude of the teacher and leader in relation to the patient. But of this point it will be more in place to speak when I come to consider the functions of the social worker as a teacher. Let us return, then, to the question, What knowledge should the social worker possess in order to do her part in the "team-work" of the medical-social dispensary? Her knowledge should approximate that of the public health officer. Like him she should be, above all, familiar with what is known to medical science about _the causes of disease_. This is of great importance because it is especially in this field of medical science and medical ignorance that the public, the patients among whom the social worker will work, is most in need both of new knowledge and of the uprooting of old error and superstition. Medical science knows very little of the causes of many diseases. But our patients, especially the more ignorant of them, are very glib and confident in their assertions as to what has caused the particular disease from which they just now suffer. They tell us about their "torpid livers," their "congestive chills," their "ptomaine poisonings" and the like. Their supposed but unreal knowledge is extensive and detailed. Indeed, so stubborn are their beliefs upon such matters that they often present a firm wall of resistance which must be broken down by the social worker before any truth upon these matters can be introduced into their minds.