GASTRIC DIGESTION. 55 



RENNIN OR CHYMOSIN. 



This body is classed as a coagulating enzyme acting 

 upon caseinogen with the formation of an albumose-like 

 body and soluble casein. The latter in the presence of cal- 

 cium salts is precipitated in the form of a coagulum or curd 

 which is termed (insoluble) casein. 



Rennin is affected by varying conditions (temperature, 

 reaction, etc.) in a way similar to pepsin. 



Make use of the rennin solution given and prepare five 

 test-tube mixtures as follows, using in each case about 5 c.c. 

 of milk and holding them at 40 C. for fifteen minutes; 

 in each experiment add the rennin solution last. 



(a) Milk + 15 drops of 0.3% HC1. 



(6) " +1 c.c. of rennin solution. 



(c) " +1 " " " " +2 cc. ammonium 

 oxalate. 



(d) Milk + 2 c.c. of rennin solution + 5 drops 0.3% 

 HC1. 



(e) Milk + 2 c.c. of rennin solution + 10 drops 0.5% 

 Na 2 C0 3 . 



Note the results carefully. If (c) has not clotted, heat 

 it to boiling to kill the enzyme. Cool and add a few drops 

 of calcium chloride solution. What is this precipitate 

 which settles out? What are the effects of acids and alka- 

 lies on the milk alone? Why did not the milk clot in experi- 

 ment c? 



