264 PRACTICAL HISTOLOGY. [XXIII. 



254, A), with a basement membrane lined by a single layer of 

 columnar cells, tapering somewhat at their central ends, leaving a 

 small irregular central lumen. 



(c.) In each cell a crowd of dark "granules," occupying about 

 the inner two-thirds of each cell, while the outer third or zone is 

 comparatively homogeneous and free from granules (tig. 254). The 

 nuclei of the cells are apt to be obscured by the presence of the 

 granules. In the borax-carmine preparation the nuclei and granules 

 are stained red ; the outer zone, about one-third, is also stained red, 

 the inner two-thirds being either not stained or only faintly so, and 

 granular, but the granules are not so sharply denned as in the osmic 

 acid preparation. 



(d.) The ducts (few), lined by a single layer of columnar epithe- 

 lium, with very faint longitudinal striation (fig. 254, D). 



9. Active Gland (H). The cells of the alveoli are less granular, 

 so that each cell shows an outer zone with no granules, occupy- 

 ing about one-half of the cell, and an inner granular zone with 

 granules, which, however, are not nearly so numerous as in the 

 resting alveoli. The nucleus (sometimes with 

 a nucleolus and accessory nucleoli) is distinct, and 

 near the centre of the cell. It is to be noted, 

 however, that all the alveoli are not in the same 

 phase. 



pj HH9^ 10- Fresh Pancreas. A very good view of the 



I : J% granular character of the inner zone of the pan- 



Vj ^j' Iv-^ pf creatic cells is obtained by examining a piece of 



fresh pancreas e.g. ox teased in normal saline. 



FlG 'Acini~of a Fre&h It is easy to observe the difference between the 



Pancreas outer homogeneous zone and the inner granular 



one. Many of the granules are liberated in the 



process (fig. 255). 



11. Injected Pancreas (L). Study a section with its blood- 

 vessels injected. It is very vascular, and in the inter-tubular cell 

 clumps are groups of capillaries. It is best injected with a Berlin- 

 blue gelatine mass from the thoracic aorta. 



C 



ADDITIONAL EXERCISES. 



12. Active Mucous Gland. The student should examine a section of a sub- 

 maxillary gland (dog), which has been in action for several hours. He cannot 

 without a license prepare such a gland for himself. It is prepared, however, 

 by stimulating at intervals for several hours the chorda tympani of a dog. In 

 this way the gland is kept secreting, or it may be stimulated by injecting 



