The Action of Tliyroid upon the Orjjans of the White Rat 217 



The enormous heart produced in rats by proloncjed thyroid-feeding is 

 especially interesting. It is alleged to occur in " Kropfherz," and is some- 

 times a feature of Graves' disease in man. Excess of thyroid stimulates 

 an excess of adrenalin, but whether the adrenalin takes any part in the 

 production of the cardiac hypertrophy is not proved. The administration 

 of adrenalin in (Jraves' disease is sometimes of great benefit in temporarily 

 allavin<r the cai'diac symptoms, slowinjj and steadying the heart beat, and 

 constricting the peripheral blood-vessels. It would appear from this that 

 the production of adrenalin is a compensatory phenomenon, its object 

 being to overcome the etiects of thyroid upon the circulation. In my series 

 of rats the animals which showed the fewest symptoms and maintained 

 their health most completely during thyroid administration were those in 

 which the suprarenals contained the largest amount of adrenalin. The 

 supi'arenals of male rats respond in this respect to thyroid more readily 

 than those of female rats, and it is interesting to note that the males 

 appear to be less susceptible to the influence of thyroid than the females. 

 In the female rats which showed the greatest susceptibility to thyroid the 

 adrenalin of the suprarenals was lowest ; in those females which showed 

 no adverse symptoms the adrenalin content was very high. It looks, 

 therefore, as though a greater secretion of adrenalin is a necessity for 

 the maintenance of health whenever there is an increase of thyroid in the 

 body. A combination of these factors may be at work in the production 

 of cardiac hypertrophy ; increased metabolism must also take some part 

 in bringing about the condition. 



The hypertrophy of the kidneys appears to be directly related to the 

 hypertrophy of the heart, and a close correlation between the two is 

 obvious from my figures. It is probable, therefore, that the kidney hyper- 

 trophy is dependent upon the same factors as those which bring about the 

 cardiac enlarcrement. 



The constant and great enlargement of the pancreas is chiefly one of 

 the glandular acini, as was pointed out by Kojima. It is not necessarily 

 a.ssociated with an increase in the intake of food, although this commonly 

 occurs in rats fed with small amounts of thyroid. It is not unlikely that 

 the internal secretion of the pancreas is increased. I have never met with 

 glycosuria in rats fed on small doses of thyroid. The increased production 

 of adrenalin and the disappearance of glycogen from the liver seem to 

 point to a condition tending to produce glycosuria. Possibly this is pre- 

 vented by increased activity of the internal secretion of the pancreas. 



Another difficult problem raised is the check in the growth of the 

 pituitary in females shown to occur by Hatai as the result of exercise, 

 and by Hoskins and myself in thyroid- feeding. In the male no such 

 check but rather an accelerated growth of the pituitary is found to occur 

 by Hatai, and by Hoskins. My results show an increase in growth of 

 the pituitary in males when reckoned in terms of percentage body weight, 

 but a decrease in size when estimated in term of percentage body length. My 



