SALIVA AND SALIVARY DIGESTION. 71 



once with ether, and the filter placed in a desiccator for 

 twenty-four hours. 



1. A small portion of the chalky-white substance is treated 

 with water: it swells up and becomes glassy without dis- 

 solving; on the addition of a drop of caustic soda solution it 

 gradually dissolves. This solution gives the biuret reaction 

 with caustic soda and a little copper sulphate solution. 



2. Boil for a few minutes, in a test-tube with dilute hydro- 

 chloric acid (one part hydrochloric acid to two to three parts 

 of water), the greater part of the substance obtained, cool, 

 then make alkaline with caustic soda, add a little copper sul- 

 phate solution and heat to boiling: precipitation of cuprous 

 oxide, which is more noticeable when the tube is cooled in 

 water. The reducing substance split off by boiling the mucin 

 with hydrochloric acid is not sugar 1 (mucose of Fr. Miiller). 



III. DETECTION OF POTASSIUM SULPHOCYANATE. 



Add one drop of hydrochloric acid to a small quantity of 

 the saliva, then a few drops of a very dilute solution of ferric 

 chloride, and shake thoroughly: red coloration in consequence 

 of the formation of soluble ferric sulphocyanate, Fe(SCN) 3 . 



IV. DETECTION OF PTYALIN. 



One gram of starch is made into a paste with 100 cc. of 

 water (for details of the method see the chapter on Pancreas, 

 page 76). 



1. After it has cooled to about 40 add to about 10 cc. of 

 the paste approximately 1 cc. of saliva, and shake thoroughly. 

 The mixture becomes clearer and thinner after a few minutes. 

 To a part of the solution obtained add a drop of iodine solu- 

 tion (iodine dissolved in an aqueous solution of potassium 

 iodide): no blue coloration, but either a red color (due to 

 erythrodextrin) or merely a yellow color from the iodine. 



1 It is chitosamine, see Zeitschr. f. Biolog. 42, 468 (1901). 



