1192 ENZYMES OR SOLUBLE FERMENTS. 



Traces of pepsin and other enzymes are frequently found in 

 urine. 



Trypsin. 



The proteolytic enzyme of pancreatic juice. The compo- 

 sition of the enzyme as prepared by Kiihne was found to be 

 remarkably complex, as shewn by the fact that when dissolved 

 in water and boiled it is split up with the formation of 20 p.c. 

 coagulated proteid and 80 p.c. albumose. 



Preparation of solutions of trypsinfor digestion experiments. 

 The following method due to Kiihne yields an extraordinarily 

 pure and active tryptic solution ; unfortunately it is a some- 

 what lengthy process. 



One part by weight of pancreas which has been extracted with 

 alcohol and ether is digested at 40 for 4 hours with 5 parts of -1 p.c. 

 salicylic acid. The residue after being squeezed out is further di- 

 gested for 12 hours with 5 parts of -25 p.c. Na 2 C0 3 , and the residue 

 is again squeezed out. The acid and alkaline extracts are now 

 mixed together, the whole made up to '25 -5 p.c. NagCOg, and 

 digested for at least a week in presence of -5 p.c. thymol. By this 

 means all the first formed albumoses are fully converted into pep- 

 tones ; this is essential. At the end of the week the fluid is allowed 

 to stand in the cold for 24 hours, filtered, faintly acidulated with 

 acetic acid and saturated with neutral ammonium sulphate. By this 

 means all the trypsin is separated out and may be collected on a 

 filter, where it is washed with the ammonium salt (sat. sol.) till free 

 from peptones. It is now finally dissolved off the filter in a little 

 25 p.c. solution of Na^C^, to which thymol is added and thus an 

 extremely active and very pure digestive solution is obtained. Ten 

 grams of the original pancreas yield 80 100 c.c. of extract. 



Although trypsin exhibits its hydrolytic powers to the 

 greatest advantage in presence of an alkali, its activity is 

 scarcely so directly related to the alkali as is that of pepsin to 

 dilute hydrochloric acid. Thus it will digest proteids, although 

 much more slowly, in a neutral solution and even in presence 

 of dilute (-012 p.c.) hydrochloric acid, but the slightest excess 

 (1 p.c.) of the acid destroys it. 



This comparative independence of tryptic activity in its 

 relations to the reaction of the digestive mixture is doubtless 

 of considerable physiological significance. The reaction of the 

 contents of the small intestine is very variable. The chyme as 

 discharged from the stomach is of course acid, and this acidity 

 is largely diminished by the advent of the strongly alkaline 

 bile and pancreatic juice, so that the reaction may become 

 alkaline within a short distance of the pylorus. On the other 

 hand the alkaline reaction may not be at all appreciable until 

 the lower end of the intestine is reached and frequently, at 



