The great book of Andreas Vesalius of Brussels, the De humani corporis fabrica, Basle, 1543, uniquely ushered in modern science and medicine. Because of the overwhelming power and significance of this masterpiece there is a tendency to dismiss his other writings as minor and of no significance. The late Charles Singer, in a discussion on the philosophic background of Vesalius, states without equivocation, "Vesalius is a man of one book," and he continues, "One may almost say that he is a book for, despite all that is written on him, his personality is very dim."1 This categorical statement by Singer displays an unwonted degree of myopia in this eminent medical historian. However, if we wish to study either Vesalius or his book, the so-called minor works become of great importance for they disclose with great clarity not only the personality of the author but, even more importantly, the forces