PHYSIOLOGICAL CHEMISTRY 389 



it can digest proteins only feebly, because it does not contain active 

 trypsin but only its zymogen trypsinogen. To convert the trypsinogen 

 into trypsin, mixture with succus entericus is necessary. The succus 

 entericus contains a substance called enterokinase which activates the 

 trypsinogen. 



There are three active ferments in pancreatic juice, one proteolytic 

 trypsin ; one amylolytic amylopsin or amylase ; one steatolytic 

 steapsin or lipase. 



I. Trypsin. Like pepsin, this ferment hydrolyses protein, and leads 

 to the production of proteoses and peptones. In this case, however, 

 digestion is more complete. Under suitable conditions the proteoses 

 and peptones can disappear entirely, polypeptids, amino acids and 

 hexone bases resulting; the ultimate decomposition products are, in 

 fact, almost the same as when a strong acid is used as the hydrolysing 

 agent (see Proteins, p. 299). 



EXPERIMENT I. A solution of pancreatic extract in 1 % sodium 

 carbonate is prepared (Liq. Pancreaticus (Benger), diluted thirty times 

 with 1 % sodium carbonate solution). In order to study the action of 

 this on proteins, add to it a piece of fibrin which has been soaked over 

 night in 1 % sodium carbonate solution, and place on a water-bath at 

 body temperature. 



The following points of difference may be noted between this and 

 the peptic digestion of fibrin: (1) The reaction is alkaline; (2) there 

 is no preliminary swelling of the fibrin ; it is gradually eaten away 

 (erosion) ; (3) when the piece of fibrin has nearly disappeared remove 

 a sample of the digest, and neutralise with weak acetic acid. A pre- 

 cipitate of alkali metaprotein results (for Reactions, see p. 310). 



Apply to another sample the tests for proteoses and peptones, and 

 note that they are positive. 1 



EXPERIMENT II. If the pancreatic extract in Experiment I. be 

 boiled before the fibrin is added, no digestion will result. The digestive 

 agent is, therefore, a ferment which is destroyed by heat. 



EXPERIMENT III. Repeat Experiment I., making the reaction acid 

 by means of hydrochloric acid. Note that, although the fibrin becomes 

 swollen up as this depends on the acid, not on the ferment no forma- 

 tion of proteoses or peptone occurs. The trypsin cannot act in acid 

 medium, being destroyed in this reaction. 



(4) Trypsin can carry digestion further than pepsin. 



Leucin, Tyrosin and the other Products of Tryptic Digestion. 

 During digestion of protein by trypsin a number of amino acids are 



1 No primary proteose is formed by tryptic digestion ; there is, however, a 

 considerable amount of secondary proteose (see p. 386). 



