derings in the labyrinth of the metaphysics of physiological science, he did enough to deter any one from attempting to tread such barren ground again. In his work on the Heart and Blood, Harvey had all the essential facts of the subject clearly before him, and he used them at once in such masterly-wise, that he left little or nothing for addition either by himself or others. Secure of his footing here, he could well dispense with "vital spirits," "innate heat," and other inscrutable agencies, he could leave "adequate and efficient causes," and other metaphysical phantoms on one side—it was physics that he was dealing with, and the physician was at home. With the information we now possess, we see clearly how indifferently weaponed was the physiologist of the year 1647 for encountering such a subject as Animal Generation; a Leeuwenhoek and a De Graaf, a Spallanzani and a Haighton, a Wolff, a Purkinje, a Von Baer, a Valentin, a Rudolph Wagner, a Bischoff, and many more, had successively to appear, before the facts of the subject could be ascertained, and a Schleiden and a Schwann were further necessary as ultimate interpreters of the things observed before they could be either rightly or wholly understood. No wonder then that The Physiologist of the 17th century, meets us in the guise of one rather puzzled with the burthen he has made up his mind to bear, and, contrary to his former wont, eking out the lack of positive knowledge by reiterated disquisitions on topics where certainty is unattainable.
It is rather curious, moreover, to find Harvey, in his work on Generation, not entirely escaping the pitfall of which he was so well aware, and which he shunned so successfully in his earlier production. In the work on the Heart, he sets out with the certainty that the whole of the notions of the ancients on the heart and blood are untenable; and then, taking Nature for his guide, his fine intellect never once suffers him to stray from the right path. In the book on Generation, on the other hand, he begins by putting himself in some sort
