Physiology and biochemistry in modern medicine . clearly established that the very earliestsign of goiter is a diminution in the iodine content of the gland; fol-lowed by an increase in the epithelial cells and in the blood supply and adecrease in the colloid. Such hyperplasia may be induced in what re-mains after removal of a large part of a normal gland (compensatoryhyperplasia), or if a similar operation be performed early in pregnancy,the young when born will be found to have hyperplastic thyroids. Acertain degree of hyperplasia exists as an accompaniment of pregnancy, i ill THYROID \.\l&g
Physiology and biochemistry in modern medicine . clearly established that the very earliestsign of goiter is a diminution in the iodine content of the gland; fol-lowed by an increase in the epithelial cells and in the blood supply and adecrease in the colloid. Such hyperplasia may be induced in what re-mains after removal of a large part of a normal gland (compensatoryhyperplasia), or if a similar operation be performed early in pregnancy,the young when born will be found to have hyperplastic thyroids. Acertain degree of hyperplasia exists as an accompaniment of pregnancy, i ill THYROID \.\l> PARATHYROID GLANDS 75] and it can be produced in normal animals (particularly rats) by placingthem on an excessive meal diet. Important observations bearing on thispoint have been made by .Marine on brook trout, ill which it lias beenfound that the so-called carcinoma that develops when the fish kept inhatcheries arc fed with unsuitable food and overcrowded, is really atypical hyperplasia. In its second stage Ibis develops into what is known. Fig. 193.—Microphotographs of thyroid gland of dog. A, normal hyperplasia; B, active hyper-plasia; C, colloid goiter. (From Marine and Lenhart.) as colloid goiter which is produced by a deposition of colloid materialbetween the rows of cells so as to cause an opening out again of thevesicles (Fig. 193)., with a consequent tendency to a reversion to thenormal histologic structure, so far as this is possible. The vesicles insuch a gland are of enormous size, and the lining epithelium, low cubical,or almost flat in shape. The outstanding characteristic feature of the colloid material is that 752 THE END0CRIN] ORGANS, OR DUCTLESS GLANDS it contains iodine, which exists in combination with a nonprotein nitrog-enous base, ami is usually called iodothyrin. In the gland itself theiodothyrin may be in combination with protein, forming iodothyro-globnlin. E. C. Kendall79 has recently succeeded in isolating a purecrystalline substance of perfect
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