2O6 COMPOSITION OF THE DIGESTIVE JUICES. [CH. VIII. 



of a millimetre scale and a magnifying glass. T W = the amount 

 of protein digested (D). Take the average for the two tubes. D 

 varies as the square root of the amount of ferment present. 



N 

 NOTES. Filtered gastric contents should be diluted with HC1 in the 



proportion of i cc. of gastric contents to 15 cc. of acid. 



For practice use a 0-5 per cent, solution of commercial pepsin in HC1. 



Dilute i, 4, and 9 cc. to 16 cc. with HC1. The amounts of egg-white 

 digested should be as V? : Vj : Vg i.e. as i : 2 : 3. 



252. The estimation of Pepsin by Calcified Milk. 



Preparation of the milk. To 50 cc. of fresh milk add 10 cc. of N. 

 calcium chloride (5-55 per cent.), and make the volume up to 100 cc. 

 with distilled water. 



Method. Measure 5 cc. of the calcined milk into 4 or 5 rather 

 wide test-tubes and place them in the warm bath at 38 C. Add 

 i cc. of the enzyme solution to one of the tubes, mix by placing the 

 thumb on the top of the tube and giving one shake ; immediately 

 replace the tube in the bath and note the time. Examine the tube 

 at intervals, and note the time when a precipitate appears. With a 

 0-5 per cent, solution of commercial pepsin it is almost instantaneous. 

 If the clotting time is very short, dilute i cc. of the enzyme with 9 or 

 19 cc. of distilled water ; mix well, wash out the pipette, and repeat 

 the test. Continue to make further dilutions of the solution thus 

 obtained until the clotting time is between ij and if minutes. 



Calculation. The suggested unit is the amount of pepsin that 

 will clot 5 cc. of the calcined milk in 100 seconds. The clotting time 

 is inversely proportional to the amount of enzyme present. 



Thus, suppose i cc. of a i in 120 dilution clots in 85 seconds, 

 then i cc. of the original solution contains 



100 

 120 x - - = 141 units. 



85 



NOTE. It is convenient to use a deep water bath with the bulb of an 

 electric lamp dipping into the water. The tubes are contained in a wire basket 

 fastened to the inner side of the bath. After the enzyme has been added, the 

 tube is held in a sloping position and gently rotated backwards and forwards. 

 The formation of the precipitate can be readily detected in the light_from_the 



