WE have seen in the first chapter of this book that the symptoms of old age may appear in quite young persons after changes in the ductless glands, especially the thyroid, ovaries, testicles, etc. We have also shown how these glands influence the condition of the tissues, and our external appearance, our immunity from infections and intoxications, and the condition of our nervous system and mind. We have also seen how these wonderful glands influence the length of our life and our prospects of a green old age, and thus it is evident that these glands are in close relation with the origin of old age. It is justifiable, therefore, to enter fully into a discussion as to whether old age is really due to degeneration of the ductless glands, which supposition must have occurred to anyone who has read the previous chapters of this book. Sir Victor Horsley, of University College Hospital, London, was the first to bring old age into causal relation with degeneration of the thyroid, and after him Vermehren and Ewald of Berlin. In a communication we made to the Biological Society at Paris, December 4, 1907, we showed that old age is not alone due to degeneration of the thyroid, but to changes in several ductless glands, of which the chief are the thyroid, ovaries, testicles, adrenals, and pancreas. In a communication to the International Medical Congress in Lisbon, in 1902, we added to these glands the liver and kidneys, which also possess an internal secretion. Let us now see if there is any evidence in support of such a statement. As we shall show, such proofs do exist and they are of a pathological, anatomical, experimental, and clinical nature. To begin with, it is a well-established fact that at a certain age the different ductless glands show important changes, notably an increase of connective tissue, with subsequent degeneration of the secreting tissue. Sir Victor Horsley[141] found that the thyroid gland, after a certain age, shows an increase of connective tissue, with fatty degeneration of the epithelium and shrinking (concentration) of the contents of the follicles. Hale White[142] also, examining at autopsy seventy thyroid glands, found an atrophic condition in old subjects, an atrophy which is more marked the older the subject, and that these changes are already present in the thyroids of persons fifty years old. Footnote 141: “On the Thyroid and Pituitary Bodies,” British Medical Journal, 1890, and Proceedings of the Royal Society, 1886. Footnote 142: Hale White: Med.-Chirurg. Transactions, vol. lxxi, 182. The thyroid, together with the parathyroids, have been found degenerated in old age by Erdheim.[143] Bauman found only very little iodine in the thyroid of aged persons. Footnote 143: Beiträge zur path. Anatomie, xxxiii, p. 158, 1903.