Sect. V, 1922 [57] Trans R.S.C. 



XI. Acceleration of Growth and Regression of Organ-Hypertrophy in 

 Young Rats after Cessation of Thyroid Feeding. The Production 

 of Tetany in Rats hy Thyroid Feeding. 



By A. T. Cameron, F.R.S.C, and J. Carmichael 



(Read May Meeting, 1922) 



(From the Department of Biochemistry, University of Manitoba) 



When thyroid tissue is* fed to young animals (rats, rabbits) the 

 rate of growth is slowed (2) and at the same time certain body- 

 organs (heart, liver, kidneys, adrenals, pancreas, etc.) hypertrophy, 

 while, if the thyroid dose be sufficiently large, there is a definite 

 slowing of the growth of the thyroid gland, which appears anaemic, 

 and enters into a resting condition (12, 10, 2). These effects, which 

 can be produced even in the adult rat (6), are definitely traceable 

 to thyroxin, the essential secretion of the thyroid (3), are not produced 

 by iodide (2), nor by parathyroid (4), nor by administration of other 

 internally secreting glandular tissue (12), nor can they be attributed 

 to a high protein diet (2, 4). 



Hewitt has recently carried out an experiment which seemed to 

 show that the effect on organ-hypertrophy was only temporary, and 

 that after cessation of thyroid feeding there is a return towards 

 normal proportions (11). As his conclusions were based on results 

 with but five rats, and these from different litters, although these 

 results were in good agreement, we have thought it desirable to carry 

 out some further experiments of this nature; these were designed to 

 ascertain in addition the effect of cessation of thyroid feeding on 

 total growth. 



During the past year we have completed six series of experiments 

 on 43 white rats (20 males and 23 females) from six litters. In these 

 17 rats were used as controls, and the remainder fed thyroid. 



In each series rats of the same age and sex were compared, 

 some receiving a diet of unlimited bread and milk plus a daily dose 

 of desiccated thyroid, based rigidly on the actual body-weight, the 

 others, bread and milk only. We have shown elsewhere that the 

 addition of a corresponding amount of liver or muscle tissue is with- 

 out effect (2), and no such addition was made to the diet of the 

 controls in these experiments. The thyroid was mixed to a paste 

 with a little flour and water, and fed on a watch-glass in the morning 



