FOOD AND DIGESTION. 381 



sometimes seem to be mere masses of protoplasm with nuclei undifferen- 

 tiated into cells. These nests of cells are sometimes seen to consist of 

 distinct columns of cells. No distinct basement membrane, however, 

 can be made out as bounding these columns. The special form of nerve 

 terminations, called Pacinian corpuscles, are often found in the pancreas. 

 The Pancreatic Juice. The secretion of the pancreas has been 

 obtained 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 removed 

 from an animal killed during digestion possesses the active properties of 

 pancreatic secretion. It is made by first dehydrating the gland, cut up 

 into small pieces, by keeping it for some days in absolute alcohol, and 

 then, after the entire removal of the alcohol, by pounding up these 

 pieces into a pulpy mass and placing 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 the removal 

 from the body often appears to contain none of the ferments. This 

 seems to indicate that the conversion of zyrnogen 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 conversion of the one into the 

 other only takes place by degrees. Dilute acid appears to assist and 

 accelerate the conversion, and if a recent pancreas be rubbed up with 

 dilute acid before dehydration, a glycerin extract made afterward, even 

 though the gland may have been only recently removed from the body, 

 is very active. 



Many other vehicles may be employed instead of glycerin, e.g., brine, 

 chloroform, water, dilute methylated spirit acidulated with acetic acid. 



Properties. Pancreatic juice is colorless, transparent, and slightly 

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

 1030, according as it is obtained from a permanent fistula then more 

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

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

 16 to 50 per thousand. It is characterized by having three distinct and 

 important enzymes known as trypsin, amylopsin, and steapsin, whose 

 action is, respectively, proteolytic, amylolytic, and lipolytic (fat-split- 

 ting); there is also a fourth distinct, though less important, one known 

 as glucase, which inverts the disaccharides. 



