The science of life : fully illustrated in tone and line and including many diagrams

WEARING OUT OF MACHINE AND ITS REPRODUCTION

Effects produced by an over-active thyroid are seen in the disease known as exophthalmic goitre. There is quickening of the pulse, and even palpitations ; there is also wasting, anda curious bulging of the eyes. We do not therefore recommend our readers to try the effect of thyroid extract without proper medical supervision.

The thyroid is not essential to life. Lite and its oxidations continue even when the whole thyroid is removed, but they continue very sluggishly; the rate of oxidation falls to about sixty per cent. of its normal value, and the temperature tends to be subnormal. The thyroid hormone acts like a draught to the fire of life. The draught is necessary to get a bright fire ; but without it, the fire will still smoulder on. From another point of view, the thyroid is Nature’s device for drugging the higher animals up to a pitch of activity not found in lower forms. The proper growth of our body, the full activity of our mind, is only possible when the thyroid is pouring its little daily dose into our system.

The pituitary gland is a small, reddish-grey eggshaped body, about half an inch across, and projecting from the middle of the lower

which, however, is far more marked in the long bones of the limbs than in the trunk. Most of the giants of fairs and circuses owe their peculiarity to this cause, while the fat lady in the next booth gains her living through a deficiency of the other part of the same minute gland. If over-activity of the gland does not begin until full stature has been reached, the bones cannot grow in length, and the excess growth takes place mainly in the hands, feet and part of the skull, giving rise to a disease called acromegaly. Not only the bones, but the tissues over them enlarge, so that the unfortunate patient gradually acquires a coarse, heavy expression, as well as having to discard his or her gloves and boots from time to time for larger sizes. The bones of the fingers usually develop abnormal bony outgrowths. The pre-pituitary affects not only growth, but also

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surface of the brain, with Fig. 66. Three photographs of the same woman showing how overthe substance of which it is gctiyity of the front part of the pituitary gland (see Fig. 36) may

continuous, into a little cup in the base of the skull. It is made up of two distinct halves, each of which produces its own secretion and exerts its own influence on the working of the body.

The hinder half or post-pituitary is mainly concerned with the body’s chemistry and chemical supply. Its secretion excites and augments the movements of the bowels, keeps the blood-vessels toned up, and stimulates the kidneys to do their work. In addition if it is deficient, the utilization of sugar by the body is disturbed. A high proportion of the carbohydrate consumed is turned into unnecessary fat instead of being used as fuel ; the result is great obesity and an exaggerated appetite, especially for sweet things.

The front half or pre-pituitary, on the other hand, is mainly concerned with growth and development. Over-activity of the pre-pituitary (such as occurs when a tumour grows in the gland), if it occurs before the bones have “set”? and finished their growth in length, results in an overgrowth of the whole body, especially in height,

gradually affect the physique.

Left to right, at twenty-five, twenty-six, and forty-two years of age. (Courtesy of Sir A. CG. Geddes and‘ Fournal of Anatomy and Physiology.”’)

stimulates the development of the reproductive organs.

When the pre-pituitary is deficient, children do not grow up properly ; they remain undersized, though of perfect proportions, and they fail to mature sexually, giving one of the most typical pictures of what is called infantilism.

The pituitary also helps to regulate temperature. Human beings with deficiency of the pituitary as a whole are generally sub-normal in temperature, and in addition often somnolent to excess. Add to this the tendency to lay on fat and the enormous appetite, and we realize what an excellent picture of an under-pituitaried individual Dickens gave us in the fat boy in Pickwick.

These effects of pituitary and thyroid have been turned to account by Nature. To prepare hedgehogs and dormice and other hibernating mammals for their winter sleep, thyroid and pituitary become damped down. Fat is put on, the creatures grow sluggish,

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