414 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



stomach and rapidly reaches its maximum two or three hours thereafter. 

 Toward the fifth or seventh hour it decreases in activity, and about 

 twelve hours after feeding again becomes increased in amount, the second 

 increase being apparently coincident with the escape of the acid chyme 

 into the small intestine. The cells of the pancreas also undergo marked 

 histological changes during the period of active secretion. .In the pan- 

 creas of a fasting dog two zones may be recognized, the inner zone highly 

 granular in nature, and with difficulty stained with carmine, and a smaller 

 homogeneous outer zone which readily stains red. The nucleus, which is 

 generally irregular in shape, lies between these two zones (Fig. 161). If, 

 on the other hand, a microscopic inspection be made of an animal in full 

 digestion, the outer homogeneous zone will be found to have greatly in- 



FIG. 162. PANCREAS OF THE DOG IN THE FIRST STAGE OF DIGESTION. (Heidenhain.) 



creased in extent, while the inner granular zone will be almost absent, 

 the whole cell being smaller and readily stained with carmine (Fig. 162). 

 After digestion has been completed, the appearance described in the fast- 

 ing cell will be again regained (Fig. 163). It would appear from these 

 facts that the secretion of the pancreatic juice is formed at the expense 

 of the granular material found in the inner zone of the secreting cells, 

 while these granules result from the amorphous homogeneous matter 

 found in the external zone, and which during digestion is built up from 

 the matter taken from the blood. We have already alluded to the fact 

 that to obtain an active pancreatic extract the gland must be taken from 

 an animal in full dig'estion, and that if the gland of a fasting animal be 

 rubbed up with glycerin and acetic acid, the glycerin extract from such 

 a gland will be strongly proteolytic. These results are to be explained, 



