It cost him "some perplexity to make the decision." He thought he saw that such an instructorship "might easily grow into a permanent biological appointment, to succeed Wyman, perhaps." At first he resolved "to fight it out on the line of mental science," feeling that "with such arrears of lost time behind [him] and such curtailed power of work," he could no longer "afford to make so considerable an expedition into the field of anatomy." But when he then considered himself as a possible future teacher of philosophy, he was overwhelmed by a feeling which he recorded on a page of his diary: "Philosophical activity _as a business_ is not normal for most men, and not for me.... To make the _form_ of all possible thought the prevailing _matter_ of one's thought breeds hypochondria. Of course my deepest interest will, as ever, lie with the most general problems. But ... my strongest moral and intellectual craving is for some stable reality to lean upon.... That gets reality for us in which we place our responsibility, and the concrete facts in which a biologist's responsibilities lie form a fixed basis from which to aspire as much as he pleases to the mastery of universal questions when the gallant mood is on him; and a basis too upon which he can passively float and tide over times of weakness and depression, trusting all the while blindly in the beneficence of nature's forces, and the return of higher opportunities." Accordingly he determined to give himself to biology, reporting to his brother Henry, who was at that time in Europe, "I am not a strong enough man to choose the other and nobler lot in life, but I can in a less penetrating way work out a philosophy in the midst of the other duties...." * * * * * As the summer went on, he still had misgivings that he would not be strong enough to prepare and conduct the laboratory demonstrations necessary for a large class in comparative anatomy and physiology. He saw that his first year of teaching had been "of great moral service to him," but thought that in other ways the strain and fatigue had been a brake upon the rate of his wished-for improvement. He therefore made up his mind to postpone the instructorship for a year and go abroad once more. These hesitations, and a few months in Europe, marked the end of the period of morbid depression through which the reader has been following him. He returned to America eager for work. Meanwhile parts of four letters written while he was abroad may be given. _To his Family._ ON BOARD S.S. SPAIN, _Oct. 17, 1873_.