118 DIGESTION 



2) Non-penetration of membranes by colloids (starch, al- 

 bumin) except peptone: Proceed as in 1). 



3) Absorption (Osmosis): 



a) Place 2 grapes, 2 raisins, 2 cranberries or other similar 

 fruit into glasses containing hot water and allow to stand for 

 an hour. Compare the fruits with untreated specimens. 



b) Prepare a syrup of 2 parts of sugar to 1 of water, bring; 

 to a boil, and stir in fruit as in a). Let stand for an hour;, 

 compare with a) and with untreated fruits. (If difference is. 

 not sufficiently obvious, allow to stand over night.) 



Note in both a) and b) changes in size and consistency, and 

 infer what has caused results in each case. Record all observa- 

 tions in schedule form, using the following signs: diminu- 

 tion ( ); increase (-f-)j no change ( ) ; solution in water 

 (dissol.). 



4) Effect of saliva: 



a) Prepare proteid, fat, and boiled and raw starch paste, by 

 mixing in test tubes with water to which 1-3 in bulk of saliva 

 has been added. Place in water bath, shake frequently, and 

 watch progress. 



b) Mix a little saliva with 3 or 4 volumes of thick starch 

 paste and note its immediate effect. 



c) Test results of salivary digestion in a) for starch, 1 sugar 

 and peptone. 2 



5) Effect of artificial gastric juice: 



1 Test by putting 1 drop of solution on a white plate and adding 

 a drop of the iodine solution. A brownish color indicates dextrin, 

 a partially digested starch. 



2 Biuret test for peptones: Put % in. of solution to be tested for 

 peptone into a test tube. Add an equal amount of sodic hydrate 

 solution, mix thoroughly, and then add 1 or 2 drops of very dilute 

 copper sulphate solution. Violet color indicates peptone. 



