Physicians who have derived their knowledge from books, and from the lectures of their teachers, must find it difficult to change their opinions in reference to obesity. With the public, when any one is told that the imbibition of large quantities of water is productive of fat, and that feeding upon animal food induces leanness, a similar degree of doubt is excited as when Galileo asserted that the sun did not revolve around the earth. On the publication of the first edition of my treatise upon Obesity, I experienced a degree of impatience, and even irritation, in view of the systematic opposition which a self-evident truth received at the hands of the medical profession. At the present time, however, I calmly recognize that the same happened in the case of every attempted innovation. I call to mind how Galileo endangered his very existence. Vesalius, the founder of anatomy, was saved from the stake only by the interference of his sovereign. Harvey, the discoverer of the circulation, was compelled to seek royal protection from the attacks of the medical men of his day. Peysonnel, a physician of Marseilles, and a great naturalist, devoted himself to the study of corals and madrepores. In 1727, he laid before the Academy of Science a monogram, proving to demonstration that corals and madrepores are structures due to animal life; that what Dioscorides, Pliny, Linnæus, Lamarck, Tournefort, &c. &c. had thought to be flowers, are in truth animals; and that these living creatures constructed and augmented their abodes; the Academy, like most learned bodies, admitted as truth only that which it taught, and consequently paid no attention to this memoir, which, nevertheless, was destined to produce an entire change in a large department of natural history. When, long afterwards, Trembley published his discoveries on fresh-water polypes, the studies of Dr. Peysonnel in this direction were remembered, and naturalists were forced to admit that the physician of Marseilles was right in maintaining that what had been taken for flowers are in reality animals. His claim as the discoverer of a fact which was destined to effect an important revolution in an extensive department of natural history, has since then not been disputed, nor could it be. All men, and men of science especially, require time before yielding to evidence, when that evidence is in opposition to preconceived views, and interferes with personal interest.