You are expected to be able to turn quickly to any medicines needed in emergency, and you soon learn to remember them and where they are placed by the arrangement into classes or kinds, which most hospitals require. Cathartics are together, hypnotics together, etc. So when you want _cascara_ you associate it with cathartic and turn to that shelf. You learn very soon that poison medicines are kept apart from the others, and quickly associate the _poison_ label with danger to patients, necessity of locking safely away and hiding the key from any but those responsible for the care of the sick. Learning to look closely at the patient's face, instead of casually glancing at her when you care for her, makes it possible for you to note changes of expression, heightened color, dilated pupils, a trace of strain, etc. Then try to find the exact word that will express what you see. Such experiments in perception and attention, association and memory, repeatedly demanded of yourself--_i. e._, the being able to recall and describe in detail the room- or ward-arrangements and to place the patients accurately, as we have just described--will prove invaluable practice, helping you to attend to every change in your patient's demeanor and expression, which may prove significant symptoms. And remember that while the mind can only contain so many isolated facts, yet there is no limit to its possibilities when the power of association of ideas is employed. Your first step to clear thinking is accuracy of perception, with attention to the thing reason chooses; your second is association of the things perceived, a grouping of them to fit in with each other, and with what is already in the mind. And both imply the third--concentration, aided by emotion and will. For passive attention and haphazard associations assure the opposite of clear thinking. CONCENTRATION _How to Study._--You learn sooner or later from experience that the quickest and best way to learn anything new is to give it your undivided attention at the moment; to perceive one thing at a time and to perceive it as something that is definite, or as some quality that is unblurred. One of you will spend three hours on an anatomy lesson, another two hours, while a third nurse may give it a half-hour of concentrated study and know it better than either of you, if you have been day-dreaming, or talking, or rebelling at the "luck" which keeps you indoors learning about bones, when the tennis-court is so inviting. True, some minds have better natural equipment and some have better previous training than others. But the average mind could learn a lesson well in much less time than is spent upon learning it poorly. Few people hold their attention strictly to the task at hand if something more interesting beckons, or if they feel tired, or "blue." But you can learn to do it.