206 ACTION OF SALIVA. 



line medium, not at all in an acid medium, or in too strong 

 an alkaline medium; 4, that it has almost indefinite power, 

 if the product of its own action (sugar) is not suffered to 

 accumulate. In all these respects, with the exception of the 

 third, the salivary ferment resembles ferments in general, 

 which are destroyed by heat, delayed by cold, and are limited 

 in their action only by the accumulated product of such 

 action." WALLER. 



Ptyalin is a type of a group of bodies called Unorganized 

 Ferments, or Enzymes. These ferments are the agents that 

 produce the peculiar chemical changes that are the chief part 

 of digestion. 



EXPERIMENTS WITH THE DIGESTIVE LIQUIDS. 



Label all the test tubes used in these experiments. 

 The action of the Saliva on starch. 



1. Make a starch paste as follows : Place one gram of 

 starch in a mortar, and rub up well with a little cold water. 

 Add two hundred c. c. of boiling water, and boil for some 

 time, stirring well. 



2. Prepare a solution of grape sugar by crushing a few 

 raisins and soaking them in water. To half a test tubeful of 

 this solution add three or four drops of solution of caustic 

 potash and two or three drops of a dilute solution of copper 

 sulphate (blue vitriol) ; or, instead of using the caustic potash 

 and copper sulphate, use " Fehling's test tablets," which can 

 be bought of the druggist. Shake the liquid and boil. An 

 orange-red precipitate indicates the presence of grape sugar. 



3. Collect a teaspoonful of saliva in each of five test 

 tubes ; add water till the tubes are half full. Label the tubes 

 A, B, C, D and E. Boil the liquid in test tube A. 



4. Add a few drops of the starch paste to each of the 



