68 THE ROYAL SOCIETY OF CANADA 



the hearts of the six animals which survived to the end of the experi- 

 ment. It should be remembered that thyroid-feeding had ceased for 

 18 days. Professor Boyd's report is as follows: 



"Areas somewhat resembling those described by Hashimoto, 

 but smaller, were observed in the hearts of rats 1 and 3 (control 

 animals) and 9 (thyroid-fed). I do not regard these bodies as of 

 any pathological importance. They are composed of elongated, 

 epithelial-like cells. The nucleus of these cells is distinct, large, and 

 vesicular, resembling the nuclei of the surrounding muscle fibres. 



"I am of the opinion that we are dealing with a small bundle of 

 heart muscle fibres, somewhat compressed, and showing some de- 

 generation of the cytoplasm, which renders the nuclei unduly distinct." 



Rats 1 and 9 appear to have been hyperthyroid rats ; rats 5 and 

 7, both thyroid-fed, showed none of these areas. Our results are not 

 in good agreement with those of Hashimoto, but the experiments 

 cannot be regarded as exactly parallel. We hope to obtain fresh 

 evidence on this point in subsequent work. 



Tetany 



In this paper we have described a number of fresh cases of 

 tetany in young rats which can be directly traced to thyroid-feeding. 



So far, in this laboratory, we have records of 193 young rats, of 

 which 65 have been used as controls, 72 have been fed thyroid, 17 

 thyroxin, 10 parathyroid, 4 large doses of liver, 10 sodium iodide, 9 a 

 vitamin-deficient diet, and 6 this diet plus thyroid. Of these rats 

 there have died, during the feeding experiments 1 control (cause 

 unascertained), 21 during thyroid feeding, 1 on a vitamin-deficient 

 diet plus thyroid, and 1 during thyroxin treatment. Tetany was 

 observed in 6 fatal cases, suspected in 7 others, and observed in a 

 further 4 cases, which recovered. These were all thyroid-fed (or 

 thyroxin-fed) rats. No tetany was observed or suspected in the 

 other fatal cases. Records of 12 adults rat (5 controls, and 7 thyroid- 

 fed) show no tetany. Among the large number of rats reared in the 

 laboratory but not used specifically in any experiment no case of 

 tetany has ever been noticed. Most of the remaining fatal cases due 

 to thyroid-feeding occurred in experiment 8 (2), with half-grown rats 

 fed heavy doses for fairly long periods. 



The cases of tetany are summarized in Table IV. 



