Besides acquiring all that she can learn of the causes and prognosis of disease, the social worker should be familiar with the symptoms of the more important and _common types of disease_. There are now several books written particularly with the object of conveying to social workers and others such knowledge as I have referred to, yet without any pretence of equipping the person either for nursing or for the practice of medicine. I will mention here a book by Dr. Roger I. Lee, Professor of Hygiene in Harvard University, "Health and Disease: Their Determining Factors" (Little, Brown & Co., Boston, 1917), and my own book, "The Layman's Handbook of Medicine" (Houghton Mifflin Co., Boston, 1916). In order to understand such books, and to arrange her knowledge of disease in such form that it may be easily handled, the social worker must have a slight knowledge of anatomy and physiology, so that she can arrange the symptoms of disease in connection with the different systems of organs: circulatory, digestive, respiratory, urinary, nervous, and locomotive. Finally, the social worker must know the _principles of hygiene_, in order that she may effectively combat medical quackery and the prevalent medical superstitions of the people. That portion of hygiene which is both securely founded upon scientific evidence and useful in the preservation of health, makes up only a very small body of knowledge, so that it can be easily mastered by any intelligent person. Our knowledge upon such matters as diet, exercise, bathing, sleep, ventilation, when such knowledge is both scientific and practically useful, could be written upon a very few pages. It consists largely of negatives which contradict the current superstitions. In my own work in this field I have found it essential that there should be no mystery and concealment, no obscurantism and mediæval Latin in the methods of treatment which the social worker explains or carries out under the doctor's directions. She must be able to deal with the patients frankly, openly, without concealment or prevarication. Otherwise she will not have moral force enough behind her statements to bring them home to the patient so as to secure any reform in his hygienic habits. Such reforms are difficult enough in any case. They are usually impossible unless they can be initiated by one rendered eloquent and convincing by the consciousness that she leans upon the truth and has nothing to conceal. If she has mental reservations, if she is trying to protect the authority of the physician in a statement which she does not believe to be wholly true, the force of her appeal will be so weakened that it will probably be ineffective. _Technical methods_ There are some technical processes of diagnosis and treatment which are usually carried out by the visiting nurse, but which may well be performed after a brief training by the social worker who is not a nurse. Among these are: