XI] 



ORGANS OF IXTERXAL SECRETION 



143 



state of disease, since the thjToid Avhieh is administered merely 

 takes the place of the secretion provided by a normal thyroid 

 and has no influence in restoring the diseased organ to a healthy 

 condition. Some animals do not ajipear to suffer anj^ harmful 

 effects from removal of the thjToid glands. Thus adult sheep 

 seem to remain unaffected. If hoA^ever the thyroids are extir- 

 pated from young lambs they become typical cretins and cease 

 to grow. This has been shown by Sutherland Simpson. Thyroid 

 grafts if successfully implanted may be as successful as feeding 

 with extract, but if the graft does not become permanently 



Fig. 69. Thyroidectomisecl or cretin sheep aged 14 months with normal sheep of 

 same age (after Sutherland Simpson from Schafer). 



'established' the beneficial effect continues only so long as the 

 transplanted tissue persists. The active princij)Ie of the thyroid 

 gland has not been isolated, but a substance called iodothyiin 

 Avhich contains 9-3 per cent, of iodine has been prepared, and this 

 is said in some measure to counteract the evil results following 

 upon removal of thyroid. Accessory thyroid tissue is sometimes 

 found posterior to the normal position of the thyroid, and this 

 may hypertrophy and comjDensate for the extirj)ated glands. 



