1915-16.] Effects of Thyroid-Feeding upon the Pancreas. 241 
intermission of the feeding for as long as four days, a certain number of 
mitoses are still visible. After ten days’ feeding, although, as we have 
seen, mitoses are becoming less frequent, the nuclei are often found in pairs 
as if they had recently divided. 
Another morphogenetic effect of thyroid-feeding is upon the zymogen 
granules within the pancreas cells. Normally in the rat the zymogen is 
in large amount, filling the inner zone of the alveoli. Incidentally it may 
be remarked that it is in greater quantity in those alveoli which immedi- 
ately surround the islets of Langerhans. After a few days’ feeding the 
relative amount of zymogen in the gland-cells is considerably diminished, 
although the difference between the alveoli adjacent to the islets and the 
rest is still apparent. The diminution of zymogen continues, if the feeding 
be continued, for about three weeks. After that time zymogen begins 
again to accumulate within the gland-cells, so that after a month’s feeding 
the alveoli again show abundance in the inner zone of the cells. These 
changes in the zymogen contents are well seen in preparations stained by 
Mallory’s method, which colours the zymogen granules an intense red. 
Fig. 3 is a photograph of a section of the same (thyroid-fed) pancreas as that 
shown in fig. 1, but stained by Mallory instead of by Muir’s method and 
magnified only 100 diameters ; and fig. 4 of the same (normal) pancreas as 
that shown in fig. 2, also stained by Mallory and magnified 100 diameters. 
In these photographs the red zymogen granules appear black, and contrast 
strongly with the rest of the cells. 
We have not been able to substantiate any distinct change in the cells 
constituting the islets of Langerhans as the result of thyroid-feeding. 
This work has been aided by grants from the Moray Fund for scientific 
research in the University of Edinburgh and from the Carnegie Trust of 
the Scottish Universities. 
EXPLANATION OF PLATES. 
Plate I. 
Fig. 1. Section of pancreas of white rat fed during seven days with addition of 
1 gramme dry ox-thyroid per diem to the ordinary diet. (Drawn by Mr R. Muir 
under a magnifying power of 400 diameters.) Muir’s staining method (alcoholic 
eosin and methylene blue). About ten mitoses are included in the field. 
Fig. 2. Section of normal pancreas of white rat fed without addition of thyroid 
to the ordinary diet. (Drawn by Mr R. Muir under a magnifying power of 400 
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