We owe our knowledge of the fact that there is a treatment for old age to the famous French scientist, Professor Brown-Séquard, whose father was American and who, for a time, was professor of physiology at Harvard and later a practitioner in New York which he left to become professor of physiology at the University of Paris. Although, before him, Claude Bernard, a man of no less fame, had shown the existence of internal secretions, Brown-Séquard was the first to draw practical conclusions from this fact, and the first who gave a solid basis to the doctrine of internal secretion. Brown-Séquard was the first to use the extracts of a ductless gland (the testicle) for therapeutic purposes, although thousands of years before him the Chinese had used different organs for purposes of healing, and the savages of Africa ate certain portions of their enemies—the liver and the testicles—to enhance their own courage. Brown-Séquard obtained surprising results by using the crushed extracts of rabbits, guinea-pigs, and dogs, of which we will say more in the chapter on the prevention and treatment of old age by organic extracts. Unhappily, as human nature is prone to attack every innovation or to ridicule it, in spite of the great reputation of this savant, his discoveries were skeptically received; and if the extracts of another similar gland—the thyroid—had not yielded such marvelous results, probably the author of the present work would never have had the opportunity to write on the treatment of old age with organic extracts. It has been shown by many authorities that the thyroid gland is able—as we have already mentioned several times in different parts of this book—to augment the processes of oxidation, and it has also been stated by several authorities, such as George Murray, Vermehren, Hertoghe, and Laache, that persons treated with thyroid extracts appear much younger after the treatment—sometimes, as Hertoghe mentions, ten to twenty years younger. Now, if a person suffering from complete myxœdema can obtain such a result by the use of thyroid extracts, should not a person suffering only from a partial form of the same disease be able to obtain similar results? It would be quite contrary to our physiological conceptions that a person in a bad condition of health and in physiologically inferior circumstances should benefit more, by exactly the same treatment, than another person who is in a much better condition of health. Therefore, the thyroid treatment of old age is justified. And indeed, we ourselves have seen astonishing results from thyroid treatment, not only in old people, but also in persons under 40.