GASTRIC DIGESTION 147 



9. Influence of Bile. Prepare three tubes as follows : 



(a) Five c.c. of pepsin-hydrochloric acid solution + 1/2-1 c.c. of bile. 



(b) Five c.c. of pepsin-hydrochloric acid solution + 5 c.c. of bile. 



(c) Five c.c. of pepsin-hydrochloric acid solution. 



Introduce into each tube a small piece of fibrin. Keep the tubes 

 at 4oC. and note the progress of digestion. Does the bile exert any 

 appreciable influence? How? 



10. Influence of Gastric Rennin on Milk. Prepare a series of five tubes as 

 follows : 



(a) Five c.c. of fresh milk -f 0.2 per cent hydrochloric acid (add slowly until 

 precipitate forms). 



(b) Five c.c. of fresh milk + 5 drops of rennin solution. 1 



(c) Five c.c. of fresh milk -}- 10 drops of 0.5 per cent sodium carbonate solu- 

 tion. 



(d) Five c.c. of fresh milk -f- 10 drops of a saturated solution of ammonium 

 oxalate. 



(e) Five c.c. of fresh milk -f 5 drops of 0.2 per cent hydrochloric acid. Now to 

 each of the tubes (c), (d), and (e) add 5 drops of rennin solution. Place the whole 

 series of five tubes at 4OC. and after 10-15 minutes note what is occurring in the 

 different tubes. Give a reason for each particular result. How do ammonium 

 oxalate and sodium carbonate prevent coagulation? 



1 Any good commercial rennin or rennet preparation may be used in preparing this 

 solution. 



