must be separated into several regiments, nevertheless for its edification the healing art must draw, directly or indirectly, on all natural science. Robert of Lincoln, Albert of Cologne, and all the Masters of that time studied medicine—that is τὰ φυσικά—as a solid part of knowledge, which in their apprehension was not only a whole but also a manageable whole. Even Francis Bacon did not realise fully the littleness of man in the presence of nature; he hoped that for his harvest man would on a right method—by, let us say, a reformed astrology and a reformed alchemy quickly surprise the secret of her processes: thus Bacon was the last of the Summists. With the differentiation of the several spheres of knowledge, and the perception of the vastness and variety of each, man has ceased to hold not the unity but the simplicity of nature; and he has given up summaries: the theologian rules no longer in metaphysics and psychology; the physician is no longer the only naturalist. Systems succeed each other but give each other the hand; it takes many a generation to kill a strong theory outright: realism, shaken by Roscellinus and Abélard, and scotched by Hales and Ockham, survived to mislead Harvey; and still it stretches its withered hand over us in the nursery, in the school, and in the great arguments of life[36]. Malebranche warned us against our deceptive terminology. “Ils prétendent expliquer, (he says), la nature par leurs idées générales et abstraites, comme si la nature était abstraite.” The methods of the English grammar schools are even now medieval in so far as their teaching begins, as it mostly does still, with abstract propositions. Mysticism gathered over Germany; in Paris to this day nature is constrained in the artifices of logic and rhetoric; and to this day platonism, chiefly by the influence of the Florentine humanists and perhaps of the Cambridge school of Henry More, has moulded both thought and language in England. John Hunter conceived a “materia vitæ diffusa”; and but yesterday Huxley had to say of Owen’s theory of “spermatic force” that an artillerist might as well attribute the propulsion of a bullet to “trigger force.” We profess Aristotle, and we talk Plato. Even by men of science it is daily forgotten that the only being is the particular. After the Faith then, realism—the belief in principles and kinds having external existence, and in formative essences to be reached by abstract thinking—stood another adversary against natural knowledge.