322 E. R. HOSKINS 



8. Thyroid Gland (tables 6 to 9) 



a. Controls. The thyroid of my rats cannot be compared 

 directly with that of other investigators owing to the different 

 technique with which it was removed from the body, as de- 

 scribed in 'Material and Methods.' The weight is about one- 

 third less than the Wistar norm, probably on account of removal . 

 of the capsule. There is also extreme variation in the weight of 

 this gland even in different members of the same litter. Usually 

 it appears relatively heavier in the older than in the younger 

 rats, and also slightly heavier in females. Jackson '(13) and 

 Hatai ('13) also have found the thyroid gland to be exceedingly 

 variable, so no final conclusions can be drawn as to the normal 

 weight of this gland. 



h. Thyroid groups. The thyroid gland (tables 6 to 9) shows 

 no constant changes as a result of the thyroid feeding. Any 

 effect if produced is hidden by the great normal variability. 

 In view of the great variability in the weight of this organ, final 

 conclusions in regard to the effect of thyroid feeding upon the 

 weight of the thyroid gland are not justified from the available 

 observations. 



c. Thymus, hypophysis, and pineal groups. In these groups 

 likewise the thyroid appears variable when compared with the 

 controls, and the results are not sufficiently marked or con- 

 stant to warrant any conclusion regarding the effects upon the 

 weight of the thyroid gland of feeding these substances. 



9. Thymus (tables 4 to 9) 



a. Controls. The thymus also is not to be compared very 

 closely with that described by previous workers. The usual 

 method of comparison considers the weight of the gland at dif- 

 ferent ages. Theoretically, the organ in the albino rat in- 

 creases in size gradually until at about 85 days it reaches its 

 maximum weight of 0.29 grams (Hatai '14), but as is well known, 

 many conditions influence the involution of this organ. Its 

 weight varies considerably in rats of the same size and age even 

 when the animals are apparently normal and kept under nearly 



