ENZYMES. FERMENTATION 409 



Activation by Enterokinase. Conversion of Trypsinogen into Try p sin. 

 A solution of enterokinase is prepared by making an aqueous ex- 

 tract of the mucous membrane of the upper part of the small intestine. 



(a) As substrate a capillary tube (Mett's tube, cf. p. 421) of 1-2 mm. bore 

 about 2 cm. long and filled with coloured gelatin is generally used. These are 

 prepared by drawing up hot 10 to 20 per cent, gelatin solution stained with 

 methylene blue or gentian violet into the tube, placing the tube horizontally 

 and allowing the gelatin to set. The tube is cut into pieces 1-2 cm. long. 

 They can only be used for experiments at room temperature ; at 40 the gelatin 

 melts and flows out of the tube. 



Two of these tubes are placed in each of three small conical flasks together 

 with 5 c.c. of *5 per cent, sodium carbonate solution. 



In the first is placed 1-2 c.c. of pancreatic juice or trypsinogen solution. 



In the second is placed 1-2 c.c. of pancreatic juice or trypsinogen solution 

 + a few drops of enterokinase solution. 



In the third is placed 1-2 c.c. of boiled pancreatic juice or trypsinogen solu- 

 tion and a few drops of enterokinase solution. 



The flasks are kept at room temperature for 8 to 10 hours. 



No solution or digestion of the gelatin occurs in No. i or No. 3 which 

 contained the trypsinogen or the boiled trypsinogen, but in No. 2 the gelatin 

 will have been dissolved at both ends of the capillary tube. 



(&) H. Bierry and V. Henri have shown that milk is a very sensitive 

 substrate for observing the activation of pancreatic juice by entero- 

 kinase. The mik is centrifugalised and filtered from fatty particles 

 through wet paper and is sterilised by heating. 



In four clean test tubes are placed : 



(1) 5 c.c. of milk + 5 drops of pancreatic juice. 



(2) 5 c.c. of milk + 5 drops of pancreatic juice + 2 drops of 

 intestinal extract. 



(3) 5 c.c. of milk + 5 drops of boiled pancreatic juice + 2 drops 

 of intestinal extract 



(4) 5 c.c. of milk 4- 2 drops of intestinal extract 



They are put in a water- bath at 40 for 10 to 15 minutes. No 

 change will be found to have occurred in tubes No. I, No. 3 and No. 

 4, whereas in No. 2 there is an immediate clarification of the milk, 

 which becomes transparent after the lapse of the above time. 



X. Erepsin. 



Erepsin is contained in the cells of the mucous membrane of the 

 small intestine and a solution is prepared by grinding the membrane 

 with sand and treating with water, to which I per cent of toluene has 

 been added, for 12 to 24 hours. The solution is strained from sand 

 and connective tissue through muslin. Erepsin acts upon proteoses 

 and peptones forming amino acids ; a 2 per cent, solution of Witte's 

 peptone is therefore used as substrate. 



