INANITION OF THYROID IN RATS 327 



In a later paper, A\'atson f'07 a) studied the thyroid in 20 wild 

 rats, 10 of which were killed immediately after capture and 10 

 fed bread and milk for H) weeks. The former showed large col- 

 loid-filled follicl(^s with flattened epithelium; the latter had smaller 

 follicles, with little colloid and cubical epithelium. Waters as- 

 cribes the change to the difl'erence in diet ; but here, as also in 

 his meat-fed rats, it is difficult to exclude the factor of inanition 

 (inadequate nutrition). He also failed to note that the degen- 

 eration maj^ occur ap])arently spontaneously. In another paper 

 Watson ('07 b) finds in young rats fed on oatmeal diet for sev- 

 eral weeks a marked enlargement of the thyroid (0.078 per cent 

 of the body weight as compared with 0.029 per cent in controls). 

 In some cases, the thyroid epithelial cells were swollen and 

 detached. 



Rebello and DaCosta CIO) describe the thyroid of the normal 

 rabbit as variable in structure with the occurrence of epithelial 

 desquamation and degeneration, resulting in obliteration of the 

 follicles in a manner very similar to that described above for 

 the rat. They consider this a normal physiological process fol- 

 lowing functional activity. However they find the degeneration 

 markedly increased by the injection of thyroid-proteid extracts. 

 They also observed similar degenerated areas in the thyroid of 

 a norinal young dog. 



Douglas ('15) in an extensive study of the effects of various 

 diets upon the thyroid of pigeons, chicks and rats, described four 

 types of structure, somewhat similar to those of Watson, He 

 concludes that: 



The histological ap]i;';irant'es do not represent different stages of se- 

 cretion, comparable to those of secreting glands engaged in the pro- 

 cess of digestion. Under similar conditions and in animals fed on simi- 

 lar diets, the appearances in the thyroid differ very markedly. One 

 oljserves all stages from the type with large vesicles, full of colloitl with 

 flattened cells, to that of a thyroid with no colloid and colunmar shaped 

 cells. Also the thyroid maj^ be wholly or partly disintegrated. The 

 variation in appearance of the thyroid seems to depend to some extent 

 on the nutrition, and is thus only in this way dejif ndent on the diet. 



Out of 31 rats (species not stated) with "ordinary laboratory 

 diet of bread" Douglas found the degenerati\T type of thyroid 



