The other letters we possess are mostly upon professional--physiological topics; though the one addressed from Nuremberg to Caspar Hofmann may, perhaps, be held an exception; for in this letter the manly and candid character of Harvey displays itself conspicuously. In his own city he challenges the Nuremberg professor to the proof. “If you would see with your own eyes the things I assert of the circulation, I promise to show them to you with the opportunity afforded me.” We have seen that Harvey accompanied the Earl of Arundel in his extraordinary embassy to the Emperor, in 1636, and may probably have been one of the party of which three members were barbarously murdered on their way, from Nuremberg to Ratisbon, as Crowne[63] informs us. Hence the solicitude which Hollar, the artist, who also accompanied the ambassador, informed Aubrey the Earl of Arundel expressed for his physician’s safety: “For he would still be making of excursions into the woods, making observations of strange trees, plants, earths, &c., and sometimes like to be lost; so that my lord ambassador would be really angry with him, for there was not only danger of wild beasts but of thieves.”[64] The burthen of the long and able letter to Siegel, of Hamburg, is still the Circulation. The one addressed to Morison, and the two to Horst, treat of the discovery of the receptaculum chyli and thoracic duct by Pecquet. Harvey has been held wanting to his greatness in having refused his assent to the facts of the distinct existence and special office of the lymphatic system. But, non omnia possumus omnes; Harvey had his own work laid out for him, and the lymphatic system was not a part of it. Aselli’s book on the ‘Lacteal Viens,’[65] was even published before Harvey’s own Exercises on the Heart and Blood had appeared, and must have been familiar to our physiologist; but that he failed to perceive the import of that discovery, and never inquired particularly into it, cannot surely be rightly laid to him as a charge; and then, when the newly-discovered system of vessels acquired extension from the researches of Pecquet, Rudbeck, and Bartholin, Harvey felt that he was both too old and too infirm to enter on the examination of so extensive and delicate an anatomical question. In entire consistency with his noble nature, however, and in striking contrast with his own opponents, he nowhere formally denies the existence of the new lymphatic vessels; nor does he once oppose the authority of his name to the investigation of the truth. On the contrary, he states his objections, “not as being obstinately wedded to his own opinion, but that he may show what can readily be urged in opposition to the advocates of the new ideas. Nor do I doubt,” he proceeds, “but that many things now hidden in the well of Democritus, will by and by be drawn up into day by the ceaseless industry of a coming age.”[66]