. The thyroid gland in health and disease. Fig. 49.—Section of normal thyioids isthmus from a 4-day-old rat. X case as Fig. 66. In rare cases, however, the thyroid was less severely affected than the parathyroid. In no case did any of the numerous offspring of the control animals exhibit thyroid fibrosis or parathyroid findings admit of the following conclusions :—-(a) As congenital parathyroid disease is comparatively common amongst the offspring of goitrous rats, it is presumable that it is also comparatively common amongst the offspring of goitrous human beings. EXPER
. The thyroid gland in health and disease. Fig. 49.—Section of normal thyioids isthmus from a 4-day-old rat. X case as Fig. 66. In rare cases, however, the thyroid was less severely affected than the parathyroid. In no case did any of the numerous offspring of the control animals exhibit thyroid fibrosis or parathyroid findings admit of the following conclusions :—-(a) As congenital parathyroid disease is comparatively common amongst the offspring of goitrous rats, it is presumable that it is also comparatively common amongst the offspring of goitrous human beings. EXPERIMENTAL CONSIDERATIONS 117 (/;) Congenital parathyroid disease is due to the action on thefoetal parathyroid glands of the toxic products of anaerobicorganisms absorbed from the maternal intestine. (c) Congenital goitre is due to a like cause, but the thyroidswelling may be induced by organisms capable of growth underaerobic or anaerobic conditions—the latter being the more Fig. 50.—Marked hyperplasia and fibrosis of thyroids isthmus. From a 4-day-old rat. Mother fed on fsecal filtrate before and during pregnancy. Same case asFig. 67. X 180. {d) Cretinism is due to the action on the foetal thyroidapparatus of specific poisons produced in the maternal intestine. These poisons are capable of causing complete destruction ofthe foetal gland in only a small proportion of cases. In the caseof cretin rats (fig. 34), the parenchyma cells of the thyroid and theparathyroid glands are completely replaced by fibroblasts (fig, 25).As a rule, however, less extreme degrees of thyroid defect areproduced, and it is interesting to note that the isthmus of the gland 118 EXPERIMENTAL CONSIDERATIONS is very liable to be first affected by the process. It is early con-verted into a band of fibrous tissue (figs. 49, 50), while the lobesmay be involved to a lesser degree. The failure to feel theisthmus of the gland in the human subject, which is so commonlyregarded as a test o
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