Studies on the Endocrine (Jlnnds 315 



has been maintained for several days and then left oti", a positive result is 

 still obtainable for at least as loni; as twenty-five days. A similar efiect 

 has been obtained after the administration of sodium iodide ; the iodine 

 showed itself nine hours after the dose had been given. 



Effects of Thyroid Administration on the 

 Weitrht of the Pancreas. 



I have only investigated the weight of the pancreas in a few cases. In 

 my earlier experiments I unfortunately omitted to determine this point. 

 I find that after thyroid feeding to normal rats and also to castrated rats, 

 either with an ordinaiy dose or with a somewhat increased dose, there is 

 a marked increase in the size of the pancreas. 



Donaldson (G) does not give the weight of the pancreas in his 

 work on the rat. Hoskins (7, a) determined the weights of the en- 

 docrine glands of the new-born guinea-pig both normal and as 

 affected by congenital lu'perthyroidism caused by giving thyroid 

 to the mother. Hi; found the pancreas of the new-born animal 

 under these conditions not demonstraVjly ati'ected. In a second paper 

 (7, b) he describes hypertrophy of the heart, liver, spleen, and supra- 

 renals, and some loss of fat. Herring (8) finds that in thyroid- 

 fed rats the weights of certain of the endocrine glands (the pancreas 

 was not investigated) show an increase as compared with controls. 

 He also noticed a great increase in the weight and volume of 

 the heart. 



Histological Changes in the Pancreas produced 

 by Thyroid Administration. 



These changes have been already briefly reported (1). Alterations in the 

 pancreas are produced in all the animals investigated, but are by far most 

 pronounced in the rat. The following is a brief summary of the effects 

 produced : — 



The most striking result of thyroid feeding is multiplication of the 

 alveolar cells, which soon become far more numerous and for the most part 

 smaller than normal. During the first fe\v days of thyroid administration 

 there is clear evidence of karyokinesis ; indeed, mitoses may be so abun- 

 dant that one can make out in a field of the ordinary high poAver of 

 the microscope (600 diameters) from three to six, and sometimes as many 

 as from eight to twelve, cells in mitotic division ; whereas, as is well 

 known, the normal pancreas never or hardly ever shows mitoses. Ac- 

 companying these changes there is great diminution in the amount of 

 zymogen within the cells. 



The cell-multiplication is still more marked when a second dose of 

 thyroid is administered after a few days' intermission, groups of small and 

 evidently rapidly dividing cells being produced : in these groups the 

 typical arrangement of alveoli is lost. 



