1/2 



THE VITAL PROCESSES 



iodine solution (page 136) to the solution of starch. It should turn a 

 deep blue color. This is the test for starch. 



Now collect from the mouth, in a clean test tube, two or three tea- 

 spoonfuls of saliva. Add portions of this to small amounts of fresh 

 starch solution in two test tubes. Let the tubes stand for five or ten 

 minutes surrounded by water having about the temperature of the body. 

 Test for changes that have occurred as follows : 



(a) To one tube add a little of the iodine solution. If it does not 

 turn blue, it shows that the starch has been converted into some other 

 substance by the saliva. () To the other tube add a few drops of a 

 very dilute solution of copper sulphate. Then add sodium (or potassium) 

 hydroxide, a few drops at a time, until the precipitate which first forms 

 dissolves and turns a deep blue. Then gradually heat the upper 

 portion of the liquid to boiling. If it turns an orange or yellowish red 

 color, the presence of a form of sugar (maltose or dextrose) is proved. 

 See page 136. 



2. Hold some powdered starch in the mouth until it completely dis- 

 solves and observe that it gradually acquires a sweetish taste. This 

 shows the change of starch into sugar. 



To illustrate the Action of the Gastric Juice. Add to a tumbler 

 two thirds full of water as much scale pepsin (obtained from a drug 

 store) as will stay on the end of the large blade of a penknife. Then 

 add enough hydrochloric acid to give a slightly sour taste. Place in 

 the artificial gastric juice thus prepared some boiled white of egg which 

 has been finely divided by pressing it through a piece of wire gauze. 

 Also drop in a single large lump. Keep in a warm place (about the 

 temperature of the body) for several hours or a day, examining from 

 time to time. What is the general effect of the artificial gastric juice 

 upon the egg? 



To illustrate Effect of Alcohol upon Gastric Digestion. Prepare a 

 tumbler half full of artificial gastric juice as in the above experiment, 

 and add 10 cubic centimeters of this to each of six clean test tubes 

 bearing labels. To five of the tubes add alcohol from a burette as 

 follows: (i) .5 c.c., (2) i c.c., (3) 1.5 c.c., (4) 2 c.c., and (5) 3 c.c., 

 leaving one tube without alcohol. Now add to each tube about { gram 

 of finely divided white of egg from the experiment above, and place all 

 of the tubes in a beaker half full of water. Keep the water a little 

 above the temperature of the body for several hours, examining the 

 tubes at intervals to note the progress of digestion. Inferences. 



