340 



Kojiraa 



but he arrived at the opinion that certain diets have a considerable effect 

 in modifying the histological appearance of the gland, these modifications 

 taking the form of changes in the amount of colloid or in its staining 

 afiinity with iiajmatoxylin-eosin. He also described alterations in the size, 

 shape, and number of the secreting cells, and in some instances noticed 

 pronounced changes in the size of the whole gland. 



In the following account neither post-mortem autolysis nor the effects 

 of alterations in diet upon the thyroid come into consideration, since the 

 diet was constant and the animals were examined immediately after death, 

 the thyroids being removed in the living condition and placed at once in 

 10 per cent formol. Nevertheless there is a certain variation in structure 

 of the thyroid of the white rat (male), even when fed for a considerable 

 time upon the same food. What this variation depends upon is not clear. 



Present Investigations. 



Microscopic Examination of Thyroid and 

 Parathyroid of Rat. 



Structure of the Normal Thyroid of the Rat. — Macroscopic- 

 ally the gland varies considerably in size, shape, and colour. It is 



Fig. 1.— Section showing adjacent portions of thyroid and parathyroid of normal 

 male rat, rusk-fed. Microphotograph ; magnified 200 diameters. Hsematoxylin- 

 eosin preparation. 



The thyroid vesicles contain colloid which is only faintly stained. The 

 lining epithelium cells are cubical. The parathyroid shows a comparatively 

 compact structure. 



generally of a dirty pink. Its vesicles show considerable differences in 

 size even in the same gland. Most are either spheroidal or oval ; their 



