56 Herrincr 



& 



happened for the most part to animals which were putting on weight 

 rapidly, and were in apparently good condition. In all cases of the kind 

 examined the suprarenals are hypertrophied. The most striking feature, 

 however, is the increased size of the heart. In No. 8 rat (Table IV.) the 

 weio-ht of the heart is nearly treble that of the normal animal of the same 

 body-weight, and the age of the animal is less than three months. Ex- 

 amination of the heart was unfortunately overlooked in the earlier experi- 

 ments recorded, but in the later ones the heart is found to be considerably 

 hypertrophied in the thyroid-fed animals. The increase in weight and in 

 the muscularity of the left ventricle are most striking features. Further 

 observations are being made on this condition. 



'to 



Summary of Con'clusions. 



The administration of small quantities, 0*2 to 0*5 grm., of fresh ox 

 thyroid daily to white rats increases the size and weight of the suprarenals 

 both in young and adult animals. Reckoned in mg. per 100 grm. body- 

 weicfht, the extent of the increase in the eighteen male animals examined 

 averages a figure which is equivalent to a rise in weight of from 76 to 78 

 per cent, above the normal. This is the result of feeding the animals with 

 the above-mentioned doses of thyroid for a period of from thiee to four 

 weeks. 



Both cortex and medulla participate in the enlargement, but the hyper- 

 trophy of the cortex is somewhat greater than that of the medulla. 



There is reason to believe that where accessory suprarenals are present 

 they too undergo enlargement. 



The adrenalin content of the suprarenals of the white rat increases 

 as a general rule with increase in weight of the animal. The amount 

 of adrenalin normally present is about 0*084 mg. per 100 grm. body- 

 weight. 



Feeding with thja-oid increases the adrenalin content of the suprarenals. 

 The average amount in the eiohteen animals examined averages from 

 0*049 to 0*052 mg., which is eijuivalent to a rise in weight of about 50 

 per cent. 



Owing to the relatively greater increase in weight of the suprarenals, 

 resulting from thyroid-feeding, the percentage amount of adrenalin in them 

 is decreased, though only to a small extent. 



It is probable that the adrenalin in the accessory suprarenals, when 

 these are present, is also increased. 



Rats fed with small doses of thyroid not infrecjuently die suddenly 

 when apparently thriving. In the animals examined which have thus 

 died there is great increase in the weight of the suprarenals and in the 

 adrenalin content. The heart is greatly h3'pertrophied in addition. There 

 is evidence that thyroid-feeding results in rapid cardiac hypertrophy in 

 white rats. The condition is being fyrther investigated. 



