GASTRIC DIGESTION 267 



2. Arrange six test tubes as follows, numbering them Nos. 

 1 to 6, and labelling with your name. 



1. 5 c.c. distilled water. 



2. 5 c.c. 0.2% hydrochloric acid. 



3. 5 c.c. water -f- 10 drops glycerine extract of 

 pig's stomach prepared above. 



4. 5 c.c. 0.2% HC1 -f 10 drops glycerine extract. 



5. 5 c.c. 0.2% HC1 -j- 10 drops glycerine extract, 

 boil thoroughly 3 or 4 minutes and cool. 



6. 5 c.c. 0.3% sodium carbonate -}- 10 drops glyc- 

 erine extract. 



In each tube suspend a Mett tube by means of a thread 

 supported by a match. Make sure that the Mett tube hangs 

 so that it does not touch the bottom of the test tube. The 

 digestion liquid must have free access to the egg white. Place in 

 the incubator until the next period. After a minimum time of 24 

 hours, compare the amounts of digestion in the different tubes 

 and record results. A slight digestion may be observed in No. 

 2, due to the formation of acid metaprotein. Tube No. 4 should 

 show good digestion. Tube No. 6 may show slight digestion 

 due to formation of alkali metaprotein. Why does not No. 3 

 digest ? 



b. ON MILK. The ferment rennin, by some investigators con- 

 sidered to be identical with pepsin, causes the clotting of milk 

 due to precipitation of casein. Calcium salts are necessary for 

 this process. Prepare two test tubes each containing 5 c.c. of 

 milk. 



1. To one add 3 c.c. ammonium oxalate. 



2. To the second add 3 c.c. distilled water. 



As the rennin in the glycerine extract is very likely to have 

 become inactive, powder a rennin tablet and add half of the 

 powder to each tube. 



Place the tubes in water at 40 for 20 minutes. No. 2 should 

 clot. No. 1 will fail to do so, since calcium is necessary in the 

 clotting process, and the oxalate will have precipitated it as in- 

 soluble calcium oxalate. To the oxalate tube add 3-4 drops of 



