ality, as it was manifested in the home and among the ranks of his students and associates.
In the estimation of a man's prominence it is hardly necessary to remark that the importance which he may assume is always a relative quantity. It is first roughly drawn from a direct comparison of this individual with other individual workers. It is then tempered, as we may say, by a consideration of the relation of the individual activities to the whole field of knowledge existent at that time. There may be great physiologists, great morphologists and great systematists, but the criterion invariably to be used to determine the highest rank must ever be that comprehensive vision which, as Verworn remarks, is able to grasp in a single Weltanschauung, the whole breadth and depth of natural scientific inquiry—that comprehensive analytic and synthetic quality of mind which brings isolated unities of fact into concrete principles. It is from this point of view, and by these standards that we must judge the extent and quality of the work of Johannes Müller: first examine into the relation of his activities to the field of natural science of his day; and, secondly, ascertain the relative value of his work when compared with the labors of other men whom posterity has been accustomed to hold as leaders in the rank and file of natural scientists. And yet, before we can fully understand—much less appreciate—the intrinsic worth of any phase of Müller's many-sided activity, we must first take time to examine briefly the condition of the biological science just previous to the period of Müller's greatest work.
We have already in the course of our discussion made mention of the scope and value of Haller's work in physiology; yet we may be pardoned, perhaps, if, in the present connection, we again make reference to some of the more important characteristics of his period, which extended from 1708 to 1777, and closed something over half a century before Müller's began.
As Galen, in the second century, had shown his recognition of the practical value of physiological data and had laid as a basis of medicine, the practical knowledge of vital phenomena; as Harvey, by his brilliant discovery of the circulation of the blood, temporarily revived, after a sleep of thirteen centuries, the exact experimental method in physiology; and after many other investigators had made important, though isolated, contributions to the budget of physiology, we find Haller bringing together the extensive mass of facts and theories and establishing thereby physiology as an independent science which should pursue not only practical lines for the aid to medicine, but also undertake theoretical aims for their own merit. We find many theories and speculations in the air during the period from 1750 to 1830, the latter date marking the beginning of the period of Müller's greatest activity. As a result of the microscopical observations made in last part of the seventeenth century on the development of the ovum, the theory