SALIVARY DIGESTION. 49 



and loses its opalescence ; this liquefaction is a process 

 quite antecedent to the saccharifying process which follows. 



4. Stages between Starch and Maltose. Mix some starch and 

 saliva in a test-tube as in 3 (a.) C, and place it in a water-bath at 

 40 0. At intervals of a minute, test small portions with iodine. 

 Do this by taking out a drop of the liquid by means of a glass 

 rod. Place the drop on a white porcelain plate, and by means 

 of another glass rod add a drop of iodine solution. 



Note the following stages At first there is pure blue with 

 iodine, later a deep violet, showing the presence of erythro- 

 dextrin, the violet resulting from a mixture of the red produced 

 by the dextrin and the blue of the starch. Then the blue 

 reaction entirely disappears, and a reddish-brown colour, due to 

 ery thro- dextrin alone is obtained. After this the reaction becomes 

 yellowish-brown, and finally there is no reaction with iodine at 

 all, achroo-dextrin being formed, along with a reducing sugar or 

 maltose. The latter goes on forming after iodine has ceased to 

 react with the fluid, and its presence is easily ascertained by 

 Fehling's solution. 



5. Effect of Different Conditions on Salivary Digestion. 



(a.) Label three test-tubes A, B, and C. Into A place 

 some saliva and boil it, add some starch mucilage. In B 

 and place starch mucilage and saliva, to B add a few 

 drops of hydrochloric acid, and to C caustic potash. Place 

 all three at 40 C. on a water-bath, and after a time test them 

 for sugar by Fehling's solution. No sugar is formed in 

 A because the ferment was destroyed by boiling, and in B 

 and because strong acids and alkalies arrest the action of 

 ptyalin on starch. 



(6.) If a test-tube containing starch mucilage and saliva 

 be prepared as in 3 (a.) C, and placed in a freezing-mixture, the 

 conversion of starch into a reducing sugar is arrested ; but 

 the ferment is not killed, for on placing the test-tube at 

 40 0. the conversion is rapidly effected. 



(c.) Mix some raw starch with the saliva and expose it 

 40 0. Test it after half an hour or longer, when no su 



will be found. 

 6. Starch is a Colloid, but Sugar dialyses. 



to 

 sugar 



