Studies on the Endocrine (Jlands 261 



tilthou«;h in youni^ rats of both sexes (fig. 3) there is a nicjre 

 considerable variation (37/z to 8/x); even in these there are few 

 SMKillt-r than 'j/jl, although occasionally a nucleus is seen as large as 

 lO/i. The nuclei are stained blue by Mallory and Muir, and very 

 distinctly by haBniatoxylin. The nucleus usually has a clear appear- 

 ance owing to the comparatively few and tine chromatin granules it 

 contains. The nucleoli are stained much in the same way as the 

 chromatin of the nucleus, liut with Mallory and ]\[uir they sometimes 

 appear red (Plate I., A). In some cells the nucleoli are large, and occupy 

 the middle of the nucleus: there is then a tendency of the chromatin 

 granules of the nucleus to be disposed near its periphery. The nuclei 



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u 



V* • w^ -^ %^- \% 



Fig. 3. — Section of pancreas of young rat (male). Microphotograph ; magnified 

 400 diameters. Haematoxylin preparation. 



If this figure is compared with fig. 2, which is from the gland of an 

 adult animal, it will be seen tiiat the chief difference lies in the fact that 

 the nuclei are much more variable in size ; it is especially obvious that 

 there are some of very large size. 



are situated between the outer and inner zones of the cytoplasm. 

 Zymogen granules are abundant in all alveoli, filling almost the 

 whole of the inner zone (tigs. 4 and 5). They are coloured purple-red 

 or rose-red by Mallory and Muir (Plate I., A) ; in the haematoxylin- 

 eosin preparations they are stained by eosin. In photographs they 

 come out black. In well-developed cells they form a large mass 

 within the cytoplasm. In small cells and in the cells of the alveoli 

 which are near the surface of the organ there is a tendency for the 

 granules to be more scattered in the cytoplasm and less accumu- 

 lated. Zymogen granules are always particularly plentiful in the 

 cells of those alveoli which are immediately adjacent to the islets 

 of Langerhans. 



In pregnant animals there are relatively fewer zymogen granules 

 (fig. 6) ; this is most marked in the earlier stages of pregnancy. 



