In his old age the great discoverer recorded his own attitude, as an interpreter, in the following words:-- "That freedom which I freely concede to others, I demand with good right for myself also; liberty, that is, in dealing with obscure matters, to bring forward, to represent, the truth, that which seems probable, until the falsity thereof shall clearly be established."[5] In 1636, eight years after he had published the treatise which now seems so convincing, Harvey was in Nuremberg and wrote to Caspar Hofmann, M.D., a professor of repute who lived there, offering to demonstrate the circulation to him. In his letter Harvey quotes impatient words of his German colleague, which show that in the face of proof the circulation still seemed to some men of high standing too useless to be true. Harvey says to Hofmann:-- "You have been pleased to reproach me rhetorically and chastise me tacitly as one who seems to you 'to accuse and condemn nature of folly as well as error, and to impose the character of a most stupid and lazy craftsman on her, since he would permit the blood to relapse into rawness and to return repeatedly to the heart to be concocted again; and, as often, to the body at large to become raw again; and would permit nature to ruin the made and perfected blood in order that she may have something to do.'"[6] To this attack Harvey calmly rejoins as follows, speaking of the blood:-- "As to its concoction and the causes of this its motion and circulation, especially their final cause, I have said nothing, indeed have put the subject by entirely and deliberately; as you will find set down in plain words and otherwise if you will be pleased to read again chapters VIII and IX."[7] More than twelve years later still, in defending the circulation against Riolanus, Harvey finds it necessary to say:-- "Those who repudiate the circulation because they see neither the efficient nor the final cause of it, and who exclaim '_Cui bono?_'--(As to which I have brought forward nothing so far; it remains to be shown)--plainly ought to inquire as to its existence before inquiring why it exists; for from the facts which meet us in the circulation regarded as existing, its uses and objects are to be sought."[8] In spite, however, of these disclaimers of formal position Harvey had repeatedly intimated, by the way, what was crossing his mind as to the meaning of the circulation, to set forth the proofs of which had been his main concern. Even in the eighth chapter to which Harvey appealed in support of his disclaimer Hofmann could have pointed to two passages as affording from his standpoint a basis for his attack. In the second and shorter of these two passages Harvey says of a vein as compared with an artery:--