326 C. M. JACKSON 



ill newborn and late fetuses (Zielinska '94, Elkes '03, Hessel- 

 })erg '10, Isenschmid '10, Gleim '12). 



Watson ('09) in 40 wild rats (species not stated) weighing 60 

 to 370 grams found wide variations in the thyroid structure, 

 which he described under four types. His first type presents 

 large colloid-filled follicles with flattened cells and darkly-stained 

 nuclei. His second type shows smaller follicles with small cu- 

 boidal cells with relatively little cytoplasm and with rounded 

 nuclei (appearing deeply-stained in his figure 2 A). In type 3, 

 the follicles are small, cells large with abundant cytoplasm, and 

 colloid faintly-staining. In type 4, the follicle cells are detached 

 and distorted, with pycnotic nuclei and cytoplasm of variable 

 amount and appearance. Types 1 and 2 (with intermediate 

 forms) predominated in 31 of the 40 glands, type 3 in 5 and type 

 4 in 4 cases. 



Watson concluded that these variations found in thyroid 

 structure ^'have been induced by dietetic or other factors in the 

 animal's environment." He thought that they did not repre- 

 sent different stages of functional glandular activity (related to 

 digestion), since they were not correlated with the nature of the 

 stomach contents. He does not mention the possibility of in- 

 anition, which according to my results might be the cause of his 

 types 1 and 2. The fact that type 1 was found in animals with 

 both full and empty stomachs does not disprove this, as the his- 

 tory previous to capture is unknown and the length of time the 

 animals were fed is not stated. Type 3 is obviously that usu- 

 ally described as normal and type 4 corresponds to the degen- 

 erative type which I have found frequently in apparently nor- 

 mal animals. 



In previous work, Watson ('05) had studied the effect of a 

 meat diet upon the thyroid gland of 12 tame rats (11 were 6 to 

 12 weeks of age, 1 adult) with 8 controls. The experiment lasted 

 6 weeks to 4 months; and the meat-fed animals were usuall}' re- 

 tarded in body weight. Ten of the 12 showed marked changes 

 in the thyroid, including congestion, epithelial proliferation of 

 the follicles and degeneration of the colloid. (Similar results in 

 meat-fed rats were obtained by Tanberg. cited by Biedl '13.) 



