2IO COMPOSITION OF THE DIGESTIVE JUICES. [CH. VIII. 



reaction of P H = 7-25, using the method described on page 277, 

 note 3. Suppose that 1-5 cc. of the soda are required. 



To 10 cc. of the diluted enzyme add half this amount of o-i N- 

 soda, mix and place the tube in the warm bath for 10 minutes. At 

 the end of the heating period add 0-75 of o-i N. HC1, mix and cool 

 under the tap. Label the tube A. 



To another 10 cc. of the diluted enzyme add 0-75 cc. of o-i N. 

 HC1, and then 0-75 cc. of o-i N. soda. Mix, and label the tube B. 

 Determine the relative clotting powers of these two solutions on 

 calcined milk as in Ex. 252. It will be found that A has almost lost 

 its action as compared with B. 



Perform a similar experiment with a solution of rennin, adding 

 the phosphate as a buffer, diluting to 100 cc. and determining how 

 much soda is required to bring it to PH = 7-25. Label the heated 

 rennin C and the control D. On comparing their clotting powers 

 as before it will be found that heating at P H = 7-25 has compara- 

 tively little effect on rennin as compared with pepsin, the clotting 

 power usually being about half that of the control. 



NOTES. i . In class work it is convenient for the Demonstrator previously 

 to determine the amounts of soda and acid required for 10 cc. of the two 

 enzymes. Otherwise the experiment takes a considerable time. 



2. If the reaction be more alkaline than PH = 7-25 the rennin is rapidly 

 destroyed. 



3. The following is the result of a typical experiment, the units being 

 calculated as explained in Ex. 252. 



F. Trypsin. 



Trypsin is the proteolytic enzyme formed by the 

 interaction of trypsinogen and enterokinase. Trypsinogen 

 is elaborated in the pancreas, and is found as such in fresh 

 pancreatic juice. Enterokinase is secreted by the small 

 intestine, but is also found in nearly all the tissues of the 



