XV.] SALIVARY GLANDS AND PANCREAS. SALIVA. 163 



cuprous oxide will be produced (Trommer's 

 test). When a very small quantity of sugar 

 is present no distinct precipitate is obtained, but 

 the fluid is decolourized or turns faintly yellow. 

 Repeat this, adding half a dozen drops of a 

 strong solution of cupric sulphate ; the reaction 

 will be much less obvious, partly owing to the 

 blue colour of the dissolved hydrated cupric 

 oxide and partly to the brown-black precipitate 

 of anhydrous cupric oxide. 



8. In this and the following experiments the saliva 1 

 used should be diluted 5 to 10 times. 

 Mix equal quantities (say 5 c.c.) of starch and 

 saliva in a test-tube and place in a water bath at 

 about 37 C. At short intervals (1 to 3 minutes) 

 take a drop of the mixture and add it to a drop 

 of iodine on a porcelain plate. The colour pro- 

 duced at first blue will later become a blue- 

 violet, a red-violet, a red-brown and a light- 

 brown yellow, according to the relative amounts 

 of starch and dextrin present, finally there will 

 be no colouration, no more starch or dextrin 

 (erythrodextrin) being left. Then divide the 

 fluid into two parts. 



1 An aqueous extract of a ptyalin-containing gland may be used 

 instead of saliva. To prepare the extract take (e.g.) the parotid 

 glands of a rabbit and having removed the connective tissue around 

 them chop them up well and place the pieces in about 200 c.c. of 

 water ; leave in the warm for an hour or two and filter. The aqueous 

 extract thus prepared contains much proteid material, and this 

 obscures the reducing action of sugar on cupric hydrate in Trommer's 

 test when a small quantity only of sugar is present. 



112 



