328 C. M. JACKSON 



only once, though it occurred frequently in pigeons and chicks. 

 It occurred very frequently (8 of 11 cases) , however, among rats 

 fed various food mixtures with fat. The normal rats usually 

 presented thyroid follicles with cubical cells and a moderate 

 amount of colloid. 



The variability in the structure of the thyroid gland and its 

 physiological and pathological relations have been discussed by 

 Marine and Lenhart ('09a, '09b, '11 a, 'lib, '11 c) in a series 

 of papers. On the basis of an extensive investigation of the hu- 

 man and animal (dog, sheep, ox, pig, etc.) thyroid, they distin- 

 guish as 'physiological' the following: (1) normal resting gland, 

 with low cuboidal epithelium; (2) hyperactive stage, with hy- 

 peremia, cells becoming hyperplastic and columnar, colloid dis- 

 appearing; (3) colloidal stage (of recovery), in which conditions 

 again return to (1) with abundant colloid. If hyperactivity^ con- 

 tinues without rest, however, colloid disappears and the cells die 

 of exhaustion, becoming progressively degenerated and desqua- 

 mated with varied degrees of disintegration. The nuclei in this 

 case are described as enlarged, often hyperchromatic, and quite 

 variable in appearance. Similar desquamation and degeneration 

 of the follicular epithelium is described in normal senile atrophy. 

 The flattened type of epithelium, indicating a minimum func- 

 tional activity, may be experimentally produced l\y administra- 

 ^tion of iodine in the diet; whereas a diet without iodine induces 

 [the columnar, hyperactive type of thyroid cells. 



The variability in structure due to the extremely sensitive 

 nature of the thyroid gland is emphasized by Marine and Len- 

 hart ('11 c) as follows: 



It has lonji; been recognized and frequently emphasized by us that 

 the thyroid tissue is extremely labile — reacting; quickly to relatively 

 slight physiological variations in the body metabolism, and for this 

 reason may show ev(^n daily histological changes within narrow limits. 



Marine ('15) also notes that thyroid glands imdergo autolysis 

 j in a few hours after removal from the body, especially if kept 

 I near the body temperature, resulting in desciuamation of the 

 alveolar epithelium. 



