. The thyroid gland in health and disease. Fig. 5.—Section of thyroid gland of healthy laboratory rabbit. There aresome slight evidences of previous hj^perplasia in the gland, a frequent finding inanimals confined in cages. x 166. which changes are indicative of an attempt at increased activityon the part of the gland, which is followed by degenerativechanges in the parenchyma cells, atrophy, and it may be a dimi-nution in size of the whole organ (figs. 5, 6). The parathyroidsare affected by inanition in like manner to the thyroid (Jackson).Lack of oxygen also produces very similar changes, as
. The thyroid gland in health and disease. Fig. 5.—Section of thyroid gland of healthy laboratory rabbit. There aresome slight evidences of previous hj^perplasia in the gland, a frequent finding inanimals confined in cages. x 166. which changes are indicative of an attempt at increased activityon the part of the gland, which is followed by degenerativechanges in the parenchyma cells, atrophy, and it may be a dimi-nution in size of the whole organ (figs. 5, 6). The parathyroidsare affected by inanition in like manner to the thyroid (Jackson).Lack of oxygen also produces very similar changes, as is tobe expected in the case of an organ whose function it is to regu-late the respiratory exchanges. For example, the experimental 38 DEFECTIVE FOOD-SUPPLY stenosis of the trachea in rats, or their confinement in an atmo-sphere deficient in oxygen, tends at first to increased activity, andlater to depression of the thyroids function. In the course of liibernation tliere is a complete disappearance. Fig. 6.—Effects of inanition oia the thyroid gland of rabbit of same age, weight,and hutch as that of Fig. 5. Note disappearance of colloid, shrinking of vesicles,relative increase of intervesicular tissue ; the size of the gland was considerablyi-educed as compared with controls. xl66. of the colloid from the vesicles and the gland becomes muchreduced in volume (Piser). That other chemical constituents of the food are no lessnecessary for the elaboration of the thyroids secretion thaniodine is highly probable. As, however, we are still ignorantof the precise chemical composition of its active principle orprinciples, we do not know what these substances are. Conditions which impair the efficient assimilation of the food,and which interfere with the chemical process of the body, willalso influence nutrition in such a way as to impair the succeeding sections examples of such conditions will be con-sidered. It is clear that those interfering with the processes ofdigcsti
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