236 THE PANCREAS. 



may be cut up finely and the enzyme extracted with glycerin, to 

 which extract a solution of sodium carbonate of from 0.2 to 0.5 

 per cent, is added. Inasmuch as the pancreas and its extracts 

 undergo putrefaction very readily, the glycerin preparation may 

 be preserved by the addition of a few drops of an alcoholic 

 solution of thymol. 



Tryptic Digestion. The differences between peptic and tryptic 

 digestion are quite marked. Pepsin requires an acid medium ; 

 trypsin acts best in one that is alkaline. When peptic digestion of 

 a solid proteid occurs, this first swells up and then gradually dis- 

 solves, while in tryptic digestion there is no preliminary swelling 

 of the proteid, but the erosion begins at once. In peptic diges- 

 tion the proteid first becomes acid-albumin, then passes into 

 the stage of primary proteoses, followed by that of secondary 

 proteoses, and finally becomes peptones. In tryptic digestion 

 it passes at once into the stage of secondary proteoses, and then 

 on into peptones. These peptones are spoken of as ampho- 

 peptones, because there are at least two of them, anti-peptone and 

 hemi-peptone. The action of pepsin stops when these are 

 formed, but trypsin can act still further by splitting up the hemi- 

 peptone into a number of substances, among them leucin, tyrosin, 

 aspartic acid, tryptophan, and lysatinin. What office these sub- 

 stances have in the body, if any, is as yet undetermined, though 

 it is probable that a portion of the urea found in the body is 

 derived from lysatinin, and Halliburton states that " recent research 

 indicates that even the simple cleavage products (leucin, tyrosin, 

 etc.) may also be utilized for the synthetic production of proteids. 



The changes which proteids undergo in tryptic digestion are 

 well shown in the following scheme of Neumeister : 



Proteid. 



Deutero-albumoses (proteoses). 



Ampho-peptones. 



.1 . ! 



Anti-peptone. Hemi-peptone, 



I.I. I I 



Leucin. Tyrosin. Aspartic Acid. Tryptophan. Lysatinin. 



Steapsin. The fat-splitting or lipolytic enzyme of the pancre- 

 atic juice, steapsin, is sometimes termed pialyn. Its action has 

 already been described in connection with saponification (p. 100), 

 and consists in the taking up of water by the neutral fats, which 

 then " split up," glycerin and a free fatty acid being the result. 



