35 



107. Test another portion of the saliva with a few drops 

 of barium chlorifle for sulphates. 



108. Dig-estive action on starch. Prepare a mixture by 

 placing- 1 g-ram of starch in a mortar and adding^ few cc. of 

 cold water, and mix well with the starch. Add 200 cc. of boil- 

 ing- water, stirring- all the while. Boi^^the fluid for a few 

 minutes. This gives a 0.5% mixture. "* 



109. Dilute the saliva with an equal volume of distilled 

 water. Label four test tubes, A, B, C, and D. Into A place 

 some saliva, boil it and later add some starch mucilag-e. In 

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

 of hydrochloric acid and to C some caustic potash. To D add 

 merely the saliva to the starch mixture. 



Place all four in a water bath not exceeding- 40° C, and 

 after a time test a small portion of them for sugar with 

 Fehling's solution. Reserve a small amount of D. Why is no 

 sugar formed in A ? In B and C a strong acid and alkali 

 arrest the action of ptyalin. Neutralize a portion of B and C 

 and test again. Is there any result ? In D the starch has 

 been converted by the ptyalin into a reducing sugar. 



110. Test portions of D with Fehling's and iodine solu- 

 tions. The absence of any blue color with the iodine indicates 

 that the starch has disappeared, having been converted into a 

 reducing sugar — maltose. Also test the remainder of A, B, 

 and C with the iodine solution. 



111. Test another portion of D with phenyl-hydrazin, 

 (71) crystals of phenyl-maltosazone should develop. Examine 

 under the microscope. 



112. The intermediate products of 'salivary digestion may 

 be detected by proceeding as in D (109) and testing a few 

 drops of the mixture every two minutes with a drop of iodine 

 upon a porcelain plate. At first there is a blue color denoting 

 soluble starch ; later there is a reddish violet color indicating 

 the presence of eryfhrodextrin ; still later there is only a slight 

 yellowish brown color, or no color at all,' when the drop of 

 iodine is added, and this indicates achroodextrin — the achromic 

 point — when a reducing sugar maltose is also present. At 

 this point the solution should reduce Fehlings. Any undi- 

 gested starch may be precipitated by alcohol which leaves the 

 maltose in solution. Saturation with ammonium sulphate 



