40 



131. Take two pieces of moist fibrin of equal size. Tie 

 one of the pieces in a bunch with thread and place it in a test 

 tube containing- some gastric extract and 0.2% hydrochloric 

 acid. Tear the other piece of fibrin into small flakes and place 

 it in another test tube with the same amount of extract and 

 acid. Let the two tubes digest at 40°C. for an equal leng-th 

 of time and note in which most dig-estion has occurred. In a 

 crude way this experiment shows the effect of mastication 

 upon g-astric digestion. Large lumps are acted upon slowly 

 and with difficulty, while an equal amount of material in a 

 state of fine division is readily digested. 



132. Rennin or chymosin is the milk-curdling enzyme of 

 the stomach. It is apparently a constant constituent of the 

 gastric juice of vertebrates. It is especially abundant in the 

 mucous membrane of the stomach of the calf (rennet). 



A solution for experimental purposes may be prepared as 

 in 120. Both rennin and pepsin go into solution. The prepar- 

 ation should not stand too long (2 or 3 days), and should be 

 neutralized with \% sodium carbonate before using-. Pepsin 

 digests rennin in an acid medicine. Commercial rennin may 

 be used in fluid or tablet form experimentally. 



133. To 10 cc. of milk in a test tube add a few drops of 

 the fluid extract of rennin or a 1 grain tablet of rennin and 

 keep the tube for some minutes at a temperature of about 

 38°C. After a short time the milk becomes solid, forming a 

 curd, and after a time the curd of casein contracts and squeezes 

 out a fluid — the whey. 



134. Repeat the experiment but first boil the rennin. 

 Compare and explain the result. 



135. Half fill a test tube with 0.2% hydrochloric acid. 

 Put in a little fibrin and add a tablet of rennin. Keep at a 

 temperature of 38°- — 40°C. for a few hours and test for pep- 

 tones and intermediate products. 



136. To 10 cc. of milk in a test tube add a few flakes of 

 commercial pepsin. Keep at a temperature of 38°C. and note 

 if there is any coagulation of the milk. See that the reaction 

 is neutral. Test also for peptones. 



