Page:The Harveian oration, 1875 (IA b22314611).pdf/21

rupturing the arteries on the other, unless the blood should somehow find its way from the arteries into the veins, and so return to the right side of the heart, “ I began,” he says, “ to think whether there might not be a motion as it were in a circle. Now this I afterwards found to be true.”

I proceed with my analysis. Harvey begins by telling us what he saw on exposing to view the heart of a living animal, especially such “ colder animals” as frogs, serpents, small fishes, snails, and the like, or such warm-blooded animals as dogs and hogs, -when the heart begins to flag. There is a time when the heart moves, and a time when it is motionless; and when it moves, it grows hard and tense, when it does not move, it is soft and flaccid. This difference may be both seen and felt in the heart of an eel taken out of the body; and, in all colder-blooded animals, the heart which grows pale as it moves, takes a deep red colour when it becomes quiescent; pale in the one case, because this motion is a muscular contraction which squeezes out the blood, red in the other, because the muscular walls relax, and the blood flows into the cavity. That this is so, is plain from the fact that