CHAP. XV.] ALIMENTATION. 173 



pancreatic juice has a far more extensive action than the 

 saliva. 



Among other important constituents the pancreatic juice con- 

 tains a ferment 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 sugar. 

 On proteids it practically exercises the same influence as the 

 gastric juice, for by it proteids are changed into peptones. 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. The pancreatic juice, in 

 thus emulsifying the fats, gives the white colour to the chyle, 

 which is its most striking external characteristic, the innumer- 

 able tiny oil-drops reflecting all the light that falls on its sur- 

 face. 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. 



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 

 containing a certain quantity of mucus. It is said to have a 

 solvent action upon all the food-stuffs, but at best its powers are 

 slow and feeble, and we have no satisfactory reasons for suppos- 

 ing that the actual digestion of food in the intestine is to any 

 great extent aided by it. 



During the passage of the food through the small intestine 

 the remaining proteids, starch, and fats are converted into pep- 

 tones, sugar, and emulsified fats or soluble soaps, and these 



