THE USES OF SALIVA. 153 



fort ; most young orators know the distress occasioned by 

 the suppression of the salivary secretion through nervous- 

 ness, and the imperfect efficacy under such circumstances 

 of the traditional glass of water placed beside public 

 speakers. The saliva also enables us to swallow dry food; 

 such a thing as a cracker when chewed would give rise 

 merely to a heap of dust, impossible to swallow, were not 

 the mouth cavity kept moist.* The saliva also dissolves 

 such bodies as salt and sugar, when taken into the mouth 

 in a solid form, and enables us to taste them; undissolved 

 substances are not tasted, a fact which any one can verify 

 for himself by wiping his tongue dry and placing a frag- 

 ment of sugar upon it. No sweetness will be felt until a 

 little moisture has exuded and dissolved part of the sugar. 

 Chemical Action of the Saliva. In addition to such 

 actions the saliva, however, exerts a chemical one on an 

 important foodstuff. Starch (although it swells up greatly 

 in hot water) is insoluble and could not be absorbed from 

 the alimentary canal. The saliva has the power of turning 

 starch into the readily soluble and absorbable grape sugar, 

 the sugar of most fruits.f The starch is made to combine 

 with the elements of water, and the final result is grape 

 sugar. 



Describe and illustrate the uses of saliva with reference (1) to 

 speech, (2) to swallowing, (3) to dissolving some foods. 



What foodstuff does saliva act upon chemically? What change 

 is produced by its action? 



* This fact used to be taken advantage of in the East Indian rice ordeal for 

 the detection of criminals. The guilty person believing firmly that he cannot 

 swallow the parched rice given him, and sure of detection, is apt to have his 

 salivary glands paralyzed by fear, and so does actually become unable to swal- 

 low the rice; while in those with clear consciences the nervous system, acting 

 normally, excites the usual reflex secretion, and the dry food causes no difficulty 

 of deglutition. 



t Grape sugar or glucose is now an extensively produced article of commerce, 

 being made for this purpose by the prolonged action of dilute acids upon 

 starchy substances. 



