There can be no doubt that Darwin had an abnormal fatigability, a lack of stamina and endurance in mental as well as physical application which plagued him from the late twenties to the sixties. As a child, he was strong and healthy, fond of outdoors, and though underrated by his teachers, noted to be possessed of intense curiosity, especially concerning natural objects. At school he was a fleet runner and cultivated a habit of long walks. Then he was surely no neurasthenic. Three years which, he himself afterwards said, were worse than wasted, at Cambridge, were filled with shooting, riding and hunting. His good health lasted until the time he probably stopped growing at 21 or 22. Thereafter his troubles began. What was Darwin, so far as his endocrine composition was concerned? In the first place his father was a variety of pituitocentric, of the post-pituitary inferior type, six feet two inches tall, exceedingly corpulent, and, in the eyes of his son, the sharpest of observers and the most sympathetic of men. He wished to make a physician out of his son in order to carry on the medical tradition of the family: Erasmus Darwin was a physician before him. His son, however, showed no inclination for so learned and confining a profession and had to be reproached by his father in these immortal words: "You care for nothing but shooting dogs, and rat-catching, and you will be a disgrace to yourself and all your family." Cambridge came after Edinburgh, as he was rushed from medicine into the clergy. But in vain. A friendship struck up with a naturalist, Henslow, settled his career for him. Henslow heard of a trip of general exploration the ship _Beagle_ was to take and recommended Darwin as naturalist. The captain at first would not hear of the proposal because of Darwin's nose, a typical pituitary proboscis. But his prejudices were overcome, and Darwin sailed. It was upon this voyage that Darwin made himself the greatest naturalist of all time, and at the same time infected himself with the virus of neurasthenia. At Plymouth, while waiting for the ship to sail, he complained of palpitation and pain about the heart, probably due to a transient hyperthyroidism, brought on by excitement. During the voyage, which lasted five years, he was afflicted often by sea-sickness. A ship-mate relates that after spending an hour with the microscope he would say "Old Fellow, I must take the horizontal for it" and lie down. He would stretch out on one side of the table, then resume his labors for a while when he again had to lie down. Already fatigability had to be fed with rest. A serious illness that Darwin claimed affected every secretion of his body acted probably as the exhausting drain upon his adrenal potential.