Just as after extirpation of the thyroid there is an increase of connective tissue or fat in various organs and tissues (as Demange found), so in old age there arises a condition of sclerosis in the tissues and organs. On this account, strictures of the urethra are readily produced in old men who have had gonorrhœa scores of years ago. The prostate gland, owing to the abundant formation of connective tissue, will also enlarge, although usually sclerosis of an organ is accompanied by diminution in size. In the central nervous system, just as after extirpation of the thyroid, there is proliferation of neuroglia. Through destruction of the nerve cells those mental attributes arise that are deemed typical of old age: Egotism, enmity against all new ideas, conservatism, etc., which we described in our address on the origin of crime before the Philadelphia Medical Jurisprudence Society, April 14, 1907.[165] The same mental characteristics are also typical of degenerated conditions of the thyroid and pituitary body, as we have seen in a case of acromegaly whose history we owe to Dr. Dercum, of Philadelphia. Footnote 165: Journal of the Amer. Med. Assoc., May 17, 1907. To recapitulate, we may state that old age is caused by degeneration of the ductless glands, and that there exists a condition of auto-intoxication in old age. The symptoms of old age are the result of breakdown of the tissues and organs which, owing to shrinking of the blood-vessels, are insufficiently supplied with blood, and, owing to the disappearance of nervous elements, are devoid of proper nervous control. Degeneration of the ductless glands and of the organs and tissues cannot be simultaneous, for the latter are under the control of the former. These glands govern the processes of metabolism and nutrition of the tissues, and by their incessant antitoxic action protect the organism from the numerous poisonous products, be they of exogenous origin, introduced with air or food, or endogenous, formed as waste products during vital processes. After degeneration of these glands the processes of metabolism in the tissues are diminished, and there is an increase of fibrous tissue at the expense of more highly differentiated structures. The fact that the changes in the tissues are secondary and take place only after primary changes in the ductless glands, is best proved by the circumstance that they can be produced, either experimentally by the extirpation of certain of the ductless glands, or spontaneously by the degeneration of these glands in disease. Our theory as to the causation of old age by degeneration of the ductless glands has been confirmed by several writers, some of whom had no knowledge of our existing work. Thus Campbell, in July, 1905, published a short note in the _Lancet_, attributing old age to degeneration of the ductless glands, overlooking our previous communication to the Paris Biological Society.