70 THE SALIVA. 



tained through purple and red to yellow. Then the liquid 

 will reduce Trammer's reagent. Hence the starch has 

 undergone hydrolysis, passing through the dextrins to 

 sugar (maltose). 



173. Try the same experiment with unboiled starch. 

 Glucose is not formed, or, if at all, only after a long time 

 and in small amounts. 



174. Try the effect of dilute acids by diluting 1 

 cubic centimeter of concentrated hydrochloric acid with 

 150 cubic centimeters of water, then adding to the saliva 

 an equal volume of the dilute acid. This makes the acidity 

 of the whole about the same as that of the gastric juice. 

 Let the acidified saliva act on boiled starch as before. No 

 glucose is produced. 



175. Place 2 cubic centimeters of saliva in each of seven test- 

 tubes, adding 2 cubic centimeters of starch solution; both of these 

 are to be measured by a pipette. From a burette containing 0.1- 

 per-cent. HC1 run into the separate tubes 4 cubic centimeters, 2 

 cubic centimeters, 1 cubic centimeter, 0.5 cubic centimeter, 0.2 cubic 

 centimeter, and 0.1 cubic centimeter. The last tube receives no 

 acid. Let them all stand in water at body temperature. Observe 

 the changes in appearance of the solutions. At intervals remove 

 a drop of liquid from each tube by the pipette and test it with a 

 drop of iodin, making notes of the speed of digestion. When 

 a blue color is no longer produced, Trommer's test for maltose 

 can be made. Calculate the strength of acid contained in each 

 tube. 



176. Place about 4 cubic centimeters of saliva in each of 

 four test-tubes. Add from a burette or cylindrical pipette con- 

 taining 1-per-cent. sodium carbonate 1 cubic centimeter, 0.5 cubic 

 centimeter, 0.25 cubic centimeter, and 0.1 cubic centimeter re- 

 spectively, warming with boiled starch in a beaker of water and 

 noting results as before. The alkali retards digestion, but does 

 not prevent it. 



177. Try the effect of free and combined acid on ptyalin as 

 follows: In each of two tubes mix about 4 cubic centimeters of 



