Go with me as my constant companion." Regarding books, however, vade mecum indicates a small volume that fits neatly in the pocket and is presumably so useful that we want it instantly available when need arises. In contrast are the large imposing volumes on a shelf, which we may consult, but rarely and with difficulty.
A small book is often more convenient than a large book, but it does not necessarily serve the same purpose. More convenient than either is a good memory coupled with strong reasoning power. Yet medical science requires information so vast in quantity that most of it cannot readily or profitably be memorized. Normal values, formulae, constants, dosages, synonyms, reactions—the amount of such information is limitless. Since no single head can carry it all, certain particular data may be printed in a little book and carried in the pocket for immediate reference. Then, if a young