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constituents and processes of the world. It was pursued by men whom we have been taught to call philosophers; and in fact only gradually did philosophy, more properly speaking, differentiate itself from physics, that is, from the elemental attempt to observe and know the physical world. Greek philosophy was to consist of logical and metaphysical conceptions; Greek physical, or let us say specifically biological, science was to continue as observation and induction. Yet it did not part company from philosophy, and occasionally employed the same processes of logic and even metaphysics. The same men might still be both scientists and philosophers — or metaphysicians. The greatest of Greek biologists was very nearly the greatest of Greek philosophers; and Aristotle the biologist did not abjure the logical and metaphysical reasonings of Aristotle the philosopher.21
But modern biology, if we fix our eyes upon its most fecund inceptions and vigorous growth, was departmental or special from the beginning, and alien from those sweeping explanations and ultimate accountings which seemed to constitute philosophy. In this sense, neither Leonardo nor Vesalius nor Harvey was a phi-