Let us add that, luckily, not every thyroid shows important changes after the age of forty or fifty, although there is usually a slight increase of connective tissue at that age. On the other hand there are thyroids in subjects of advanced age which show no important degenerative change. This, however, is, according to our experience at autopsies, a very rare occurrence. The point of main importance is the amount of colloid substance present. A thyroid with much colloid, if it is of normal quality (which can be recognized by the way it stains with eosin), is a thyroid of good activity. As we know, the thyroid contains more iodine than any other part of the body. The main bulk of the iodine in our body comes from the thyroid. It follows from the investigations of Docent Oswald,[144] in Zurich, that the quantity of iodine in the thyroid depends upon the amount of colloid substance. Hence a thyroid with much colloid substance contains much iodine, and a large goiter composed of connective tissue alone and containing no colloid, cannot contain any iodine. Footnote 144: Oswald: Zeitschrift für physiolog. Chemie, 1899, and Virchow’s Archiv, 169, p. 444, 1902. Differing with a famous French physician who said that the age of a man depended upon his arteries, we would state that it depends upon the quality of his thyroid. For the condition of the arteries, as we have shown in different parts of this book (Chapters II and VI), depends very much upon the condition of the thyroid gland, which governs the whole circulatory system. The parathyroid glands, which are in relation with the thyroid, and changes in which may produce cramps, as shown by Jeandelize,[145] Pineles,[146] etc., also present an increase of connective tissue, with fatty degeneration of the epithelium, in old age, as was shown by Erdheim,[147] of the Vienna Pathological Institute. Footnote 145: L’insuffisance thyroidienne et parathyroidienne, Paris, 1904. Footnote 146: Grenzgebiete f. Med. Chirurg., 1905. Footnote 147: Erdheim: Loc. cit. As is well known, the ovaries also, between the ages of forty-six and fifty, undergo important changes and involution, with consequent cessation of the menses. There is an increase of connective tissue with degeneration of the epithelial structure. There is also a retrograde metamorphosis of the Graafian follicles into fibrous tissue. The testicles have been found atrophied in old age by Professor Langhans,[148] but there are many exceptions, as shown by S. Spangaro.[149] Footnote 148: Langhans: “Hoden Atrophie,” Handbuch der Deutschen Chirurgie, Stuttgart, 1887. Footnote 149: Spangaro: Anatomische Hefte, lx, 1902.