Harvey begins his Treatise on the movement of the Heart and Blood with the clear statement that the heart must be examined whilst it is alive; but he says, "I found the task so truly arduous and so full of difficulties that I was almost tempted to think with Fracastorius that the movement of the heart was only to be comprehended by God. For I could neither rightly perceive at first when the systole[10] and when the diastole took place, nor when and where dilatation and contraction occurred, by reason of the rapidity of the movement, which in many animals is accomplished in the twinkling of an eye, coming and going like a flash of lightning. "At length by using greater and daily diligence and investigation, making frequent inspection of many and various animals and collating numerous observations, I thought that I had attained to the truth ... and that I had discovered what I so much desired--both the movement and the use of the heart and arteries. From that time I have not hesitated to expose my views upon these subjects, not only in private to my friends, but also in public in my anatomical lectures, after the manner of the Academy of old. "These views, as usual, pleased some more, others less: some chid and calumniated me and laid it to me as a crime that I had dared to depart from the precepts and opinion of all anatomists: others desired further explanations of the novelties, which they said were both worthy of consideration, and might perchance be found of signal use." The results of his experiments soon made it plain to Harvey that the heart's movements could be studied more readily in the colder animals, such as toads, frogs, serpents, small fishes, crabs, shrimps, snails, and shell-fish, than in warm-blooded animals. The movements of the heart became more distinct even in warm-blooded animals, such as the dog and hog, if the organ was attentively noted when it began to flag. The movements then became slower, the pauses longer, so that it was then much more easy to perceive and unravel what the movements really were and how often they were performed. Careful observation and handling the heart made it clear that the organ was muscular, and that its systole was in every way comparable with the contraction which occurs in the muscles of the forearm when the fingers are moved. "The contraction of the heart is therefore of greater importance than its relaxation. During its contraction the heart becomes erect, hard, and diminished in size, so that the ventricles become smaller and are so made more apt to expel their charge of blood. Indeed, if the ventricle be pierced the blood will be projected forcibly outwards at each pulsation when the heart is tense."