58 ENDOCRINE GLANDS 



The functions of the thyroid have been elucidated by 

 the observation of the various phenomena following the 

 extirpation of the thyroid and by the physiological effect 

 of the thyroid extract and finally, by the results obtained 

 by giving experimentally excessive doses of thyroid. 



I. PHENOMENA FOLLOWING THE REMOVAL OF THE 

 THYROID. 



In animals thyroidectomy produces two types 

 of phenomena: 



1. ACUTE SYMPTOMS which consist of post operative 

 tetany and are due to the simultaneous extirpation of the 

 parathyroid glands. 



2. CHRONIC SYMPTOMS are the only ones which are 

 really due to thyroid insufficiency. They are particularly 

 marked in the young during the stage of growth. The de- 

 thyroided animals are small and deformed, as compared 

 to the controls. Their skin is infiltrated with an indurated 

 edema; at the same time it becomes dry, wrinkled 

 squamous, the hairs lose their brilliancy, and fall out. 

 The growth of bone is stopped and the genital organs 

 (testicle or ovary) become atrophic. These animals become 

 sad, slow, apathetic and appear idiotic. 



These accidents occur the more rapidly if the animal 

 is young. 



The thyroid gland, therefore, secretes a substance neces- 

 sary to the organism ; the absence causes the appearance 

 of trophic symptoms. If in a dethyroided animal a graft 

 of thyroid gland is made or it is given the extract of thy- 

 roid, these accidents are avoided. 



II. PHYSIOLOGICAL ACTION OF THYROID EXTRACT. 



Thyroid extract has a very definite effect on the blood 

 pressure, the cardiac rhythm and nutrition. Schaefer in 



