28 INTERNAL SECRETION 



Microscopic examination of the thyroid gland shows that, in 

 its finished state, it is what F. Kraus very aptly terms a " storage " 

 gland. In regard to the continuous formation of colloid, it is 

 assumed that a proportion of the secretion passes into the blood- 

 stream, though opinions differ as to the manner in which this 

 takes place. 



According to Biondi, the passage of the secretion into the 

 lymph-vessels is effected by dehiscence of the epithelial cells and 

 the breaking through of the colloid mass into the lymph-spaces ; 

 Hiirthle believes that the secretion passes out by way of the 

 intercellular passages ; while Lewandowski is of the opinion that 

 the process is osmotic. One thing, however, is certain, namely, 

 that a substance is found in the lymphatics which appears to be 

 identical with the colloid substance of the thyroid. 



Although a certain amount of information is forthcoming 

 concerning the effect which nervous excitement and other momenta 

 exercise upon the secretory process, the data are insufficient to 

 form the ground-work of a hypothesis. Hiirthle found that 

 electric stimulation of the thyroid nerves did not produce con- 

 comitant changes in the histological aspect of the secretion. 

 Katzenstein found that, after resection of the superior and inferior 

 laryngeal nerves of one side, there was histological degeneration 

 of the thyroid upon both sides. On the other hand, Martini was 

 unable to discover any departure from the normal tissue, and 

 A. Exner found that the amount of iodine in the gland remained 

 unchanged. 



Wiener has recently discovered that pilocarpin is without 

 effect upon the thyroid, while adrenalin brings about an increase 

 in the amount of thyroglobulin. Marked effects were obtained 

 with iodide of sodium, which also induced a hypersecretion of 

 thyroglobulin. In cases where the gland had previously been 

 removed, iodide of sodium not only induced a suppression of 

 compensatory hypertrophy, but it is probable that it even gave 

 rise to atrophy. The action of thyroidin, though much less in- 

 tense, was identical with that of the inorganic iodine combinations. 



According to Wyss and E. A. Schafer, the cells of the 

 thyroid gland react to pilocarpin in the same way as the cells of the 

 true secretory glands. Hiirthle described the histological signs of 

 increased glandular activity in dogs after ligature of the gall-duct, 

 and he believed that the bile, which thus passed into the blood, 

 stimulated the thyroid gland to increased secretory activity. 

 This, however, was not confirmed by Miiller's experiments with 

 cats, which were highly jaundiced as a result of the ligature 

 of the common bile duct. In dogs, ho\vever, this operation was 

 followed by enlargement of the thyroid follicles and formation 

 of tissue similar to that seen in colloid goitre. These changes are 

 attributed, by both Miiller and Lewandowski, to acute 

 degeneration of the gland. 



