true function of muscle was unknown to Aristotle (Harvey to the contrary notwithstanding),[138] and the blood-vessels were the only continuous special paths between center and periphery which Aristotle could make out. In his time, as we have seen, the nerves had not been distinguished, even anatomically, from the bands and cords of the ligaments and tendons. So, for Aristotle, the nutritive, sensory, and motor faculties, the desires and emotions, in short all the souls or parts of the soul (to use the ancient phraseology) that are not the most exalted, dwell in fire within the heart, suitably and honorably placed at the central "acropolis." To the divine mind of man, on the other hand, he does not assign a definite special dwelling-place within the body. Harvey differed often and widely from Aristotle. Yet even in his old age he wrote: "The authority of Aristotle has always such weight with me that I never think of differing from him inconsiderately."[139] Cannot one fancy, may not one conjecture, that in the eyes of the discoverer of the circulation his great discovery, fundamental, new, and original, as he rightly claimed it to be, may at times have seemed to constitute a thorough correcting and filling in of a rough sketch dashed off at the Lyceum? Let us see. Aristotle had no conception of anything resembling a circulation of the blood, nor any definite mechanical ideas as to its movement. While the vena cava as well as the aorta received blood from his valveless heart and yielded it to the body at large, blood ebbed back to the heart during sleep, and the warm nutrient liquid which the vena cava and the aorta yielded to the tissues had previously entered the heart continuously but in an imperfect state through both of these great vessels, to go forth again through both, perfected into blood and heated, with no perplexing differences of color noted between that in the great vein and that in the aorta. The relations between the food, the blood, the heart, and the body at large, though recognized to be complex, may well have presented themselves to Aristotle with something of the vagueness with which the relations between the food, the liquids, the contractile vacuole, and the living substance of a protozoön, present themselves to us. If the heart, retaining its Aristotelian powers, were found to receive the blood imperfect or impaired, but to receive it by the veins only, and to send it out, but only by the arteries, warmed and perfected or restored to perfection at its Aristotelian source; what have we but the systemic part of the circulation, as it may have pictured itself sometimes to Harvey?[140] CHAPTER V PHYSICIANS _versus_ PHILOSOPHERS--HARVEY FOR THE PHILOSOPHERS Thus it is striking to find Harvey, as the champion against Galen of a view essentially Aristotelian, entering the field of controversy where ancient Greek still met ancient Greek in the modern Europe of 1628.