SECRETIONS 99 



2. Morphological phenomena accompanying the secretion. 



The cells of the pancreatic glands have a striated outer 



and granular inner zone. During activity the striated outer 

 zone is widened, the granular inner zone decreases, while 

 during rest the opposite take place (see Fig. 5). In the 



A B 



FIG. 5. GLAND-CELLS OF PANCREAS IN DIFEERENT STAGES OF SECRETION. 



(After Heidenhain.) 



A, first stage of digestion (6-10 hours); the striated outer zone is much broader 

 than the granular inner zone. B, second stage of digestion (10-20 hours); the 

 striated outer zone is narrower and the inner granular zone is wider. 



active condition the cells are separated by sharper (frequently 

 double) boundary lines than during rest. 



3. Influence of the nervous system upon secretion. Secre- 

 tory nerves for the pancreas are supposed to be present in 

 the vagus and in the sympathetic. 



It has been stated that the pancreas of herbivorous 

 animals secretes continuously, while that of carnivorous 

 animals secretes periodically, i.e. only after the introduction 

 of food in the stomach. 



Among the substances in the stomach which can reflexly cause 

 pancreatic secretion are chiefly acids, fats, and spices. 



Concerning the effects of extirpation of the pancreas see 

 Chapter XL 



5. BILE SECRETION 



i. Composition of bile. Bile, the secretion of the liver, 

 is a reddish-yellow or green ropy substance, having an 

 intensely bitter taste. When it is poured from the liver it 

 contains about 1.5-3$ solids. During fasting the bile does 

 not flow directly into the intestine, but first into the gall- 

 bladder, where it is concentrated by the absorption of water 

 and the addition of mucus, so that it contains about 16-17$ 



