Читать книгу The Body at Work: A Treatise on the Principles of Physiology онлайн

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Iodine stored in the thyroid and parathyroid glands is distributed to all the tissues. The remarkable symptoms which indicate that the tissues are not receiving an adequate supply may occur under either of two conditions. Iodine may be deficient in the food, or the thyroid gland may be incompetent; the former is the commoner cause. And here we see the explanation of the formation of a goitre. By increasing the size of the organ which selects iodine, Nature attempts to obtain and store an adequate supply for distribution to the tissues.

Cretinism has been observed in animals. If attention were directed to this inquiry, it might be found that it is not so exceedingly rare as would be judged from the few observations that have been recorded. A cretin, if a wild animal, falls an easy prey. If a domesticated animal, little trouble is taken to insure its survival. A myxœdematous pig is a dwarf with coarse, sparse hair, thick, warty hoofs, large jowl, heavy ears. It is apathetic. A piglet presenting these characteristics is not altogether uncommon in a litter. Among chickens and pigeons, also, individuals appear which might, judging from their uncouth appearance and mental dulness, be suffering from cretinism. The only way of proving that this is the case is to feed them on thyroid glands; it does not matter from what animal the gland is obtained. Operative cretins, produced by removing the thyroid gland soon after birth, recover their natural characters on a diet containing a daily allowance of thyroid gland. The coarse hairs, or wiry towsled feathers, fall off, and are replaced by a smooth, supple growth. The thickened skin becomes soft and pliant. Mental apathy gives place to alertness. They make up for lost time by growing more rapidly than other animals of the same age, which have not been operated upon, although they never surpass the normal stature.