DIGESTION. 271 



the pancreas of a fasting dog consist of two zones, an inner or central 

 zone which is finely granular, and which stains feebly, and a smaller 

 parietal zone of finely striated protoplasm which stains easily. The 

 nucleus is partly in one, partly in the other zone. During digestion, it 

 is found that the outer zone increases in size, and the central zone 

 diminishes ; the cell itself becoming smaller from the discharge of the 

 secretion. At the end of digestion the first condition again appears, the 

 inner zone enlarging at the expense of the outer. It appears that the 

 granules are formed by the protoplasm of the cells, from material sup- 

 plied to it by the blood. The granules are thought to be not the fer- 

 ment itself, but material from which, under certain conditions, the fer- 

 ments of the gland are made, and therefore called Zymogen. The 

 special form of nerve terminations, called Pacinian corpuscles, are often 

 found in the pancreas. 



Pancreatic Secretion. The secretion of the pancreas has been ob- 

 tained for purposes of experiment from the lower animals, especially the 

 dog, by opening the abdomen and exposing the duct of the gland, which 

 is then made to communicate with the exterior. A pancreatic fistula 

 is thus established. 



An extract of pancreas made from the gland which has been re- 

 moved from an animal killed during digestion possesses the active prop- 

 erties of pancreatic secretion. It. is made by first dehydrating the gland, 

 which has been cut up into small pieces, by keeping it for some days in 

 absolute alcohol, and then, after the entire removal of the alcohol, plac- 

 ing it in strong glycerin. A glycerin extract is thus obtained. It is a 

 remarkable fact, however, that the amount of the ferment trypsin 

 greatly increases if the gland be exposed to the air for twenty-four hours 

 before placing in alcohol; indeed, a glycerin extract made from the 

 gland immediately upon removal from the body often appears to contain 

 none of the ferment. This seems to indicate that the conversion of 

 zymogen in the gland into the ferment only takes place during the act 

 of secretion, and that the gland, although it always contains in its cells 

 the materials (trypsinogen) out of which trypsin is formed, yet the con- 

 version of the one into the other only takes place by degrees. Dilute 

 acid appears to assist and accelerate the conversion.and if a recent pan- 

 creas be rubbed up with dilute acid, before de@clration, a glycerin 

 extract made afterwards, even though the gland ma^have been onlv re- 

 cently removed from the body, is very active. 



Properties. Pancreatic juice is colorless, transparent, and slightly 

 viscid, alkaline in reaction. It varies in specific gravity from 1010 to 

 1015, according as it is obtained from a permanent fisiula then more 

 watery or from a newly-opened duct. The solids varylin a temporary 

 fistula from 80 to 100 parts per thousand, and in a permanent one from 

 16 to 50 per thousand. 



