PRINCIPLES OF DIGESTION 49 



of the beakers. (This kills the protoplasm in the cells of 

 the beets without injury to the cell walls.) Add a few 

 drops of hydrochloric acid to each beaker, and then test 

 with Fehling's solution for grape sugar. In which has the 

 sugar dialyzed from the cells? In which is the water col- 

 ored? Study the arrangement of protoplasm in a dead and 

 in a living cell as illustrated in Fig. 23, and state your 

 conclusions as to the influence of protoplasm on dialysis. 



(Substances that dialyze are called crystalloids. Sub- 

 stances that do not dialyze are called colloids.) 







XXX. AN ENZYME. 



Apparatus. Ground malt, starch, test tubes, iodine solution, 

 Fehling's solution. 



Directions. Make an extract of malt diastase (an en- 

 zyme) by shaking up five grams of ground malt with 50 c.c. 

 of cold water. Let it stand for a few hours and then filter. 

 Make a thin starch paste by mixing a teaspoonful of starch 

 with a cup of boiling water. Fill two test tubes half full 

 of this starch preparation. Test a little of the starch prep- 

 aration with the iodine solution, to determine strength of 

 reaction. Test a little of the starch preparation and also 

 some of the diastase solution with Fehling's solution. Is 

 grape sugar present in either of them? Now add 10 c.c. of 

 diastase solution to one of the test tubes; heat both tubes, 

 and keep them as near as possible at a constant temperature 

 of 60 centigrade. 



At intervals of five minutes remove a little of the con- 

 tents of each tube with a pipette and test with the iodine 

 solution. Do the same, using Fehling's solution instead of 

 iodine solution. Is the amount of starch on the increase 



