In his eighteenth year he was prostrated by a disease which developed into inflammation of the lining membrane of the heart, from which he never recovered. The verdict of the physician was ever in his mind: "You may fall at any time as suddenly as from [by] a musket-shot." His life was afterwards, indeed, like the life of a soldier constantly under fire. Instead of making him a valetudinary, this continual liability to death aided to make him a hero. He acted in the spirit of his father's advice,--"If you must die, die in harness." Dr. Elder proves that his existence was prolonged by the hardihood which made him careless of death. "The current of his life shows convincingly that incessant toil and exposure was [were] a sound hygienic policy in his case. Naturally his physical constitution was a case of coil springs, compacted till they quivered with their own mobility; nervous disease had added its irritability, and mental energy electrified them. It was doing or dying, with him. And it was not a tyrant selfishness, a wild ambition, that ruled his life, but a rare concurrence of mental aptitude, moral impulse, and bodily necessity, that kept him incessant in adventure." Nothing could damp this ardor. He contracted the peculiar disease of every country and climate he visited, and was frequently on what seemed his death-bed; but no experience of physical misery had any influence in blunting his intellectual curiosity or impairing the energies of his will. One of those elastic natures "who ever with a frolic welcome take the thunder or the sunshine," his whole existence was wedded to action, and he was always ready to suffer everything, if he could thereby do anything.