One of the most noted of them was the Benedictine abbess, St. Hildegard, of Bingen on the Rhine, who was eminent not only as a theologian but also as a writer whose treatises on various branches of science are justly regarded as the most important productions of the kind during the Middle Ages prior to the time of Albertus Magnus. Besides this, she not only wrote many books on _materia medica_, on pathology, physiology and therapeutics, but, as a practitioner, she gloriously sustained the best traditions of her sex in both theoretical and practical medicine. Her work entitled _Liber Simplicis Medicinae_, which deals with what in the Saint's time was called "simples"--for the belief was then current that each plant or herb was or provided a specific for some disease--contains accounts of many plants used in _materia medica_, as well as statements of their importance in therapeutics. Her descriptions often indicate an observer of exceptionally keen perception and one whose knowledge of science was far in advance of her epoch. The same observations may be made respecting Hildegard 's work, _Liber Compositae Medicinae_, in which she treats of the causes, signs and treatment of diseases.[188] Still more remarkable, in many respects, is a treatise in nine books, entitled _Physica_ or _Liber Subtilitatum Diversarum Naturarum Creaturarum_, which, among other things, treats of the various elements, of plants, trees, minerals, fish, birds, quadrupeds, and of the manner in which they may be of service to man. Of so great importance was this book considered that several editions of it were printed as early as the sixteenth century. No less an authority than the late Rudolph Virchow, the founder of cellular pathology, characterizes it as an early _materia medica_, curiously complete, considering the age to which it belongs.[189] And Haeser, in his history of medicine, directs attention to the historical value of the book, declaring it to be "an independent German treatise, based chiefly on popular experience."