His disease advanced with steady pace, and, though there were many fluctuations, his strength continued to decline. The gradual progress of his disorder allowed him many intervals of comparative ease. In these he returned to his literary labours with his usual ardour, and wrote and translated for the press until within a few weeks of his death. Perfectly aware of the fatal character of his disorder, he watched its progress step by step with the coolness of an anatomist, while he submitted to it with the resignation of a Christian. The "Rambles of a Naturalist" were among the last productions of his pen, and were written in the intervals of acute pain and extreme debility. These essays are not inferior in poetical beauty, and vivid and accurate description, to the celebrated letters of Gilbert White on the natural history of Selbourne. He came to the study of natural history as an investigator of facts, and not as a pupil of the schools; his great aim being to learn the instincts, the structure, and the habits of all animated beings. This science was a favourite pursuit, and he devoted himself to it with indefatigable zeal. He has been heard to say that, in investigating the habits of the shrew mole, he walked many hundred miles. His powers of observation were quick, patient, keen, and discriminating: it was these qualities that made him so admirable a naturalist. His fame, however, rested chiefly, during his life, upon his success as a teacher of anatomy, and in this capacity he raised himself at once to the top of his profession. He was so intent on making his students understand him, and he was so fully master of the subject himself, that his clear and animated flow of eloquence never failed to rivet their attention; and he became, wherever he taught, the idol of his pupils. His lectures on anatomy were real analytical experiments. The subject was placed before the class; tissue and muscle and blood, vessel and bone, were laid bare in their turn, their use and position exemplified to the eye, and enforced by the most lively and precise description; while the student was at the same time receiving the most valuable lessons in practical dissection.