'260 ELEMENTARY PHYSIOLOGY less. 



Of these the chief is one which is called trypsin, and is so 

 far like pepsin that it converts proteins into peptones,' 

 but it differs from pepsin in several respects. In the 

 first place trypsin is most active in an alkaline solution, 

 such as of 1 per cent, sodium carbonate, while pepsin will 

 only act in presence of an acid. In the next place, the 

 change which proteins undergo by the action of trypsin 

 does not end with the formation of peptones, as it does 

 in the case of pepsin, but proceeds further, and some 

 of the peptone is broken down into the crystalline 

 substances known as leucine, tyrosine, and similar bodies. 

 These amino-acids are peculiarly interesting, inasmuch as 

 after absorption they are carried to the liver in the blood 

 of the portal vein and are converted in part into urea by 

 the liver (see p. 189). 



The second ferment in pancreatic juice is one which 

 resembles the ptyalin of saliva in so far as it converts 

 starch into sugar, but it acts more energetically. The 

 sugar which it produces is maltose (CjjHjoOn). 



The third ferment has no action on either proteins 

 or carbohydrates, but it acts on the ordinary fats in 

 such a way as to split them up into glycerine and 

 a fatty acid. Tlie latter uniting with the alkali of 

 the pancreatic juice forms soaps, and this process is 

 known as saponification. The soaps so formed are 

 soluble substances and therefore can pass into the wall of 

 the intestine. In this form then the fat can be absorbed. 

 Moreover, they help greatly in reducing the remaining 

 fats to that state of fine subdivision, known as an 

 emulsion,^ which, as we shall see presently, is an 

 important preliminary to the digestion of fat in the 

 intestines. 



1 An artificial pancreatic digestion of proteids may be carried on in 

 the way already described for pepsin (p. 247), using as a digestive fluid a 

 1 per cent, solution of sodium carbonate to which some of the extract of 

 pancreas sold as "liquor pancreaticns " has been added. ■ 



2 When a substance is sub-divided into extremely minute particles 

 suspended in a fl\iid under conditions such that these particles do not run 

 together on standing, the substance is said to be emulsified and the fluid 

 is called an emulsion. Thus milk is a typical emulsion. 



