CHAP. XVI.] ALIMENTATION. 195 



a filter-paper, kept wet with a solution of bile-salts, whereas it 

 will not pass, or passes with extreme difficulty, through one kept 

 wet with distilled water. 



Pancreatic juice. Healthy pancreatic juice is a clear, some- 

 what viscid fluid, with a very decided alkaline reaction. It is 

 actively secreted by the pancreas during digestion and flows 

 into the intestine in conjunction with the bile. The Germans 

 call the pancreas the "abdominal salivary gland," though the 

 pancreatic juice has a far more extensive action than the saliva. 



Among other important constituents the pancreatic juice con- 

 tains an enzyme called trypsin, which, like pepsin, has the power 

 to transform proteids into peptones ; trypsin, however, requires 

 an alkaline medium to effect this transformation, while pepsin, 

 as we have already seen, requires the medium to be acid. 



Action of pancreatic juice upon food. On starch pancreatic 

 juice acts with great energy, rapidly converting it into mal- 

 tose. On proteids it practically exercises the same influence 

 as the gastric juice, for by it proteids are changed into pepton.es. 

 On fats it has a twofold action : it emulsifies them, and it splits 

 them up into fatty acids and glycerine. If we shake up olive 

 oil with water, the two cannot be got to mix : as soon as the 

 shaking ceases, the oil floats to the top; but if we shake up 

 olive oil with pancreatic juice, the oil remains evenly suspended 

 in it. The reason of this is, that the oil has been minutely 

 divided into tiny droplets, and each droplet surrounded by a 

 delicate envelope supplied from the albumin in the pancreatic 

 juice, so that they cannot fuse together to form the large drops, 

 which would soon float to the top. 1 Secondly, the fats that are 

 not emulsified are broken up into glycerine and fatty acids. The 

 glycerine is absorbed, and the fatty acids in the presence of an 

 alkali form soaps which are soluble in water and capable of 

 absorption. It is probable that the greater part of the fat is 

 absorbed by the latter method. 



Thus pancreatic juice is remarkable for the power it has of 

 acting on all the food-stuffs, starch, fats, and proteids. 



Succus entericus, or intestinal juice. Succus entericus is a 

 clear, yellowish fluid, having a faintly alkaline reaction and 



1 The pancreatic juice, in thus emulsifying the fats, gives the white colour to 

 the chyle, which is its most striking external characteristic, the innumerable 

 tiny oil-drops reflecting all the light that falls on its surface. 



