Thus though the mixture of humours and the composition of minute parts may justly be presumed so be somewhat different in men from what it is in mere animals; and therefore any experiment we make upon the one concerning the effects of medicines will not always apply to the other; yet as the structure of the veins and muscles, the fabric and situation of the heart, of the lungs, the stomach, the liver and other parts, are the same or nearly the same in all animals, the very same hypothesis, which in one species explains muscular motion, the progress of the chyle, the circulation of the blood, must be applicable to every one; and according as it agrees or disagrees with the experiments we may make in any species of creatures, we may draw a proof of its truth or falshood on the whole.