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EFFECT ON RATS OF THYROID FEEDING 



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In spite of the possible variations in controls the results are in such 

 good agreement that the conclusion maj^ be definitely drawn that 

 during thyroid-feeding of young rats growth-rate is decreased, while after 

 cessation of such feeding growth-rate is accelerated above normal to such 

 an extent that the weights of the treated rats usually exceed those of their 

 controls in from 4 to 5 weeks after cessation of thyroid-feeding. 



The cause of this acceleration is almost certainly associated with 

 the organ-hypertrophy produced by thyroid feeding. 



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Hypertrophy of body-organs 



In the second of our series of studies of the effects of thyroid- 

 feeding (3) we have summarized (Table XXVI) the effect on the 

 hypertrophy of body-organs under the conditions of the present 

 experiments. With the preparations used, and with rats of approxi- 

 mately the same age, fed thyroid for the same period, hypertrophies 

 are to be expected of the order: liver, 50 to 100 per cent.; kidneys, 

 30 to 55 per cent.; heart, 20 to 30; spleen, 20 to 40; adrenals, 30 

 (females) to 60 (males). Other experiments have given, if anything, 

 higher results. Other observers, using larger doses, have obtained 

 distinctly greater hypertrophies (10, 12). We have shown also that 

 muscle tissue is diminished (3, 4, 5, 6) and lymphoid tissue is increased 

 (4, 6). Thyroid tissue is usually diminished in ratio by from 20 to 

 30 per cent. 



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