510 VERTEBRATE LIFE AND ORGANIZATION 



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Figure 30.2. Upper, Cells of the normal thyroid gland of the rat. Lower left, 

 Thyroid from a normal rat which had received ten daily injections of thyrotropin. 

 Lower right. Thyroid from a rat six months after complete removal of the pituitary 

 gland. (Turner: General Endocrinology.) 



tude. The Swiss surgeon Kocher removed the thyroids from a series of 

 patients and then noted that they developed the same symptoms as 

 Gull's patients. In 1895, using a newly devised calorimeter to measure 

 the rate of metabolism in patients by the amount of heat they pro- 

 duced, Magnus-Levy found that persons with myxedema (Gull's dis- 

 ease) had notably lower than normal metabolic rates. VV^hen these 

 patients were fed thyroid tissue, their metabolic rate was raised toward 

 normal. This led to the idea that the thyroid secretes a hormone which 

 regulates the metabolic rate of all body cells. It was found in 1896 that 

 the thyroid hormone contains iodine. Thyroglobulin was first isolated 

 in 1897 and thyroxin in 1914. Its chemical formula was determined in 

 1926 and it was first synthesized in 1927. 



The role of thyroid hormone in all vertebrates is to increase the 

 rate of a certain series of enzyme reactions which lead to the release of 

 biologically available energy. The amount of energy released by an 

 organism under standard conditions at rest, measured in a calorimeter 



