These are among the number of more abstruse matters, and demand your ingenuity, most learned Nardi. Nor need you plead in excuse your advanced life; I myself, although verging on my eightieth year, and sorely failed in bodily strength, nevertheless feel my mind still vigorous, so that I continue to give myself up with the greatest pleasure to studies of this kind. I send you along with these, three books upon the subject you name.[58] If you will mention my name to his Serene Highness the Duke of Tuscany, with thankfulness for the distinguished honour he did me when I was formerly in Florence, and add my wishes for his safety and prosperity, you will do a very kind thing to [58] [Nardi had written to Harvey requesting him to select a few of the publications which should give a faithful narrative of the distractions that had but lately agitated England.] Your devoted and very attached friend, WILLIAM HARVEY. 30th Nov. 1653. LETTER VI _To John Daniel Horst, principal Physician of Hesse-Darmstadt_ EXCELLENT SIR,--I am much pleased to find, that in spite of the long time that has passed, and the distance that separates us, you have not yet lost me from your memory, and I could wish that it lay in my power to answer all your inquiries. But, indeed, my age does not permit me to have this pleasure, for I am not only far stricken in years, but am afflicted with more and more indifferent health. With regard to the opinions of Riolanus, and his decision as to the circulation of the blood, it is very obvious that he makes vast throes in the production of vast trifles; nor do I see that he has as yet satisfied a single individual with his figments. Slegel wrote well and modestly, and, had the fates allowed, would undoubtedly have answered his arguments and reproaches also. But Slegel as I learn, and grieve to learn, died some months ago. As to what you ask of me, in reference to the so-called lacteal veins and thoracic ducts, I reply, that it requires good eyes, and a mind free from other anxieties, to come to any definite conclusion in regard to these extremely minute vessels; to me, however, as I have just said, neither of these requisites is given. About two years ago, when asked my opinion on the same subject, I replied at length, and to the effect that it was not sufficiently determined whether it was chyle or one of the thicker constituents of milk, destined speedily to pass into fat, which flowed in these white vessels; and further that the vessels themselves are wanting in several animals, namely, birds and fishes, though it seems most probable that these creatures are nourished upon the same principles as quadrupeds; nor can any sufficient reason be rendered why in the embryo all nutriment, carried by the umbilical vein, should pass through the liver, but that this should not happen when the fœtus is freed from the prison of the womb, and made independent. Besides, the thoracic duct