XXIIl] PANCREAS AND LIVER 181 



are not very obvious ; the nucleolus of each nucleus is 

 generally conspicuous. 



2. Section of active pancreas of a dog (alcohol) ; 

 stain with picrocarmine or hsematoxylin. The division 

 of the cells into granular and non-granular zones will 

 be seen ; the inner zone however appears as a slightly 

 stained confusedly granular mass, and does not show 

 the separate spherical granules of the osmic acid pre- 

 paration ( 1) ; the outer zone, containing the nucleus, 

 is homogeneous, or nearly so, and stains more deeply 

 than the inner zone. 



3. Examine the sections of pancreas for the inter-tubular 

 clumps. In mammals they form roundish clumps of small cells 

 generally of polyhedral outline ; they have no obvious granules, 

 and stain very little with carmine or haematoxylin. In the frog 

 the cells are elongated, and arranged in indistinct columns. 



In some of the lobules of the mammalian pancreas centro- 

 acinary cells will be seen ; these are small flattened cells 

 occurring in the part of the alveolus close to the ductule and 

 inside the secreting cells. 



B. LlVEE. 



1. Sections of frog's liver (osmic acid). Mount in 

 dilute glycerine. Observe with a low power that the 

 gland apart from the ducts and ductules consists of 

 anastomosing tubes between which the blood capil- 

 laries run. Observe (h. p.) 



The tubes. In transverse sections they are seen 

 to consist of four to six cells, each containing a large 

 nucleus in its outer portion. 



