It is easy to see that a tight collar offers difficulty to the free circulation of the blood through this gland, and therefore it is advisable to wear a loose, and also low, one. Strange to say, many ladies wear such tight, high collars, not availing themselves of their immunity from such a yoke, which men have voluntarily endured for so long a time. It is advantageous not to button both sides of the shirt-band to which the collar-stud is fastened, but one side only, which is easily done when low collars are worn and is not noticeable; the great comfort and advantage of so doing will outweigh all other considerations. The vitality of the thyroid gland may be enhanced by various measures in which thyroid secretion, or iodine—its main element,—is introduced into the body. The easiest way to effect this is by taking foods, such as plants and vegetables, which contain a maximum of iodine. The iodine in the thyroid and other parts of the body is introduced therein mainly with our food (or by drugs in the case of goiter). Another way is by taking thyroid extracts. Since, at a certain age,—as mentioned in the chapter on the causes of old age,—parts of the epithelium of the thyroid are degenerated and replaced by connective tissue, thyroid extracts will be the best means, if taken in very small doses, of supplying this physiological need. Such doses of the extracts, freshly prepared and from a reliable firm, can do no harm, but, on the contrary, will keep the thyroid in good working order. As we have learned from personal experience these very small doses can even be taken, at intervals, for a long time, without injury to the health, and we need not await the arrival of old age, but should use them as a preventative against it, and in particular temporarily where there is, or has been, a great demand for thyroid secretion, as, for instance, in convalescence after an infectious disease, or after childbirth, especially if the flow of milk is scanty, which is an expression of a defective thyroid; also after sexual excesses, and in cases of mental depression, after we have suffered grief; in fact, after any of the occurrences which we know to be harmful to the thyroid gland, which, in such cases, has been giving off larger amounts of its secretion. We must, however, caution patients against ever taking these extracts _save under medical advice_, since otherwise dangerous results may be and have been produced, as will be shown elsewhere. The diet of greatest hygienic value with regard to the thyroid will consist of large quantities of milk, with little or no meat, but plenty of vegetables. With such a diet there will result less putrefaction in the intestines, and thus also less demand for the thyroid secretion to destroy poisonous matters; at the same time, along with the milk and vegetables, iodine, the main element of the thyroid secretion, will be brought into the body, and a loss of this product from it prevented.