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in the living heart and blood, or attributable to anything "of a sublime, lucid, ethereal, celestial, or divine nature," he naturally, in the then state of scientific knowledge, failed to master the problem of the source of animal heat. This was only possible more than 200 years after his time by the discoveries of Black, Priestley, Lavoisier, and others on the nature of combustion, and by the researches of modern physiologists on the metabolism of the tissues, and the foci of heat production in the body. We now know that there is no more innate heat in the heart than is evolved by its own intrinsic muscular contractions. Neurology in Harvey's time consisted largely in speculations as to the seat of the rational soul, and the mode of generation and distribution of the animal spirits to the various organs of the body. Little or nothing was known of the relations of the heart to the nervous system. Harvey had, however, some obscure conceptions as to the difference between "natural" and animal motion. He says:—
"There are some actions and motions the government or direction of which is not dependent on the brain, and which are therefore
