[CAMERON] EFFECT ON RATS OF THYROID FEEDING 67 



to an abnormal amount of tissue catabolism and at the same time 

 such an immediate oxidation of the circulating food-units that they 

 are in great part broken down before utilization by the tissue cell. 

 This increased tissue activity calls forth a hypertrophy of all the 

 essential organs of the body, heart, liver, kidneys, adrenals, pan- 

 creas, etc., with the exception of the thyroid itself, which no longer 

 receives its stimulus to activity (probably fall of thyroxin content of 

 the blood perfusing the thyroid below some definite minimum) and 

 rests. Lymphatic tissue hypertrophies, for some reason as yet 

 unexplained. 



When thyroid-feeding ceases the body has become possessed of 

 an engine of higher power than normal. At the same time not only 

 is the thyroxin-stimulus to catabolism removed, but the thyroids, of 

 subnormal size, no longer produce their normal check to growth. 

 Growth-processes proceed at hyper-efificiency. Total growth is 

 accelerated. But the stimulus to hypertrophy of the essential 

 organs is removed, and they gradually become normal. 



It is doubtful whether the acceleration so distinctly marked in 

 certain experiments would last. It seems more likely that, with 

 heart and thyroid both approaching normal condition at the end of 

 seven weeks the growth-slope would also again become normal. 



Histological Observations 



Hashimoto (9) has shown that oral administration of toxic doses 

 of thyroid produces in nearly all cases definite heart lesions ("dense 

 accumulations of large ' histiocytare ' cells derived from the clasmo- 

 cytes present in the interstitial connective tissue, in small circum- 

 scribed areas between muscle fibres, or not infrequently near blood- 

 vessels ") . He considers that the interstitial in flammatory proliferation 

 and diffuse parenchymatous degeneration may both be attributed 

 directly to thyroid intoxication. The hearts become function- 

 ally inferior. The lesions closely resemble those described by 

 Aschoff and others in the hearts of individuals suffering from rheu- 

 matism and correspond with those in goitre hearts. Sub-toxic doses 

 give similar results in the majority of cases, though only small areas 

 are affected. 



Most of the other tissues examined showed evidence of increased 

 activity (hyperplasia). 



This paper did not come to our attention until the final experi- 

 ment was in progress. Professor Wm. Boyd, of the Department of 

 Pathology, University of Manitoba, kindly examined histologically 



