While he was in the midst of these various labours, his friends often feared for his strength, for though gradually improving in health after his first year at Cambridge, he was not robust, and from time to time he seemed on the point of breaking down. Still, hard as he was working, he was in reality wisely careful of himself, and as he grew older, paid more and more attention to his health, daily taking exercise in the form either of bicycle rides or of lawn-tennis. Moreover he continued to spend some part of his vacations in travel. Combining business with pleasure, he made frequent visits to Germany and France, and especially to Naples. The Christmas of 1876-7 he spent in Greece, that of 1878-9 at Ragusa, where his old school-fellow and friend Mr Arthur Evans was at that time residing, and the appointment of his friend Kleinenberg to a Professorship at Messina led to a journey there. Early in the long vacation of 1880, he went with his sister, Mrs H. Sidgwick, and her husband to Switzerland, and was joined there for a short time by his friend and pupil Adam Sedgwick. During this visit he took his first lessons in Alpine climbing, making several excursions, some of them difficult and dangerous; and the love of mountaineering laid so firm a hold upon him, that he returned to Switzerland later on in the autumn of the same year, in company with his brother Gerald, and spent some weeks near Zermatt in systematic climbing, ascending, among other mountains, the Matterhorn and the Weisshorn. In the following summer, 1881, he and his brother Gerald again visited the Alps, dividing their time between the Chamonix district and the Bernese Oberland. On this occasion some of the excursions which they made were of extreme difficulty, and such as needed not only great presence of mind and bodily endurance, but also skilful and ready use of the limbs. As a climber indeed Balfour soon shewed himself fearless, indefatigable, and expert in all necessary movements as well as full of resources and expedients in the face of difficulties, so much so that he almost at once took rank among the foremost of distinguished mountaineers. In spite of his apparent clumsiness in some matters, he had even as a lad proved himself to be a bold and surefooted climber. Moreover he had been perhaps in a measure prepared for the difficulties of Alpine climbing by his experience in deer-stalking. This sport he had keenly and successfully pursued for many years at his brother's place in Rosshire. When however about the year 1877, the question of physiological experiments on animals became largely discussed in public, he felt that to continue the pursuit of this or any other sport involving, for the sake of mere pleasure, the pain and death of animals, was inconsistent with the position which he had warmly taken up, as an advocate of the right to experiment on animals; and he accordingly from that time onward wholly gave it up.