546 SPECIAL PHYSIOLOGY. 



Action of the Saliva and other Fluids of the Mouth. 



The saliva, the chief fluid poured into the mouth, acts first, by its 

 watery basis, as a solvent, contributing thus also, to the perfection of 

 the sense of taste. It dissolves saline substances, the organic acids, 

 alcohols, and ethers, gum, sugar, and the soluble albuminoid and gela- 

 tinoid bodies. Secondly, and most importantly, the saliva changes the 

 starch granules, first into dextrin, and then into soluble and crystal- 

 loid dextrose, glucose or grape-sugar, ready for absorption. Dextrin 

 has the same atomic constitution as starch, C 6 H 10 5 , whilst grape 

 sugar, C 6 H 12 6 , appears to be produced from it, by the taking up of 

 1 atom of water H 2 0. No evolution of gas takes place, as occurs 

 in alcoholic fermentation. The change is more rapid than fermen- 

 tation. On adding some saliva to a weak solution of boiled starch, 

 and immediately testing it with iodine, the blue color of iodide of 

 starch fails to appear ; or, on mixing saliva with a small quantity of 

 cooked starch, already rendered blue by iodine, the color is discharged. 

 (Vintschgau.) These facts prove that the starch is changed ; its con- 

 version into sugar is shown by examination with a polariscope, or by 

 boiling the fluid, after adding a slightly alkaline solution of tartrate 

 of copper, when a yellowish-red precipitate of oxide of copper is thrown 

 down, indicating the presence of grape-sugar (Trommer's test). 



The parotid saliva is, by itself, able to convert starch into sugar ; 

 that of the submaxillary and sublingual glands accomplishes the 

 change, when combined with the mucus of the mouth, which, indeed, 

 has, by some, been regarded as the sole agent in this transformation. 

 A mixture of all the fluids of the mouth appears, however, to form 

 the most active combination for this purpose. Besides the saliva and 

 fouccal fluids, the pancreatic juice possesses this property in great per- 

 fection ; but the gastric juice and the bile do not. Most animal mem- 

 branes also, such as the mucous membrane of the mouth, intestines, 

 und even the bladder, particularly if they are in a state of commenc- 

 ing decomposition, exhibit this power. 



The constituent of the saliva to which this peculiar power of trans- 

 mutation is due, is the salivin or ptyalin, which is said to act cata- 

 lytically, or by presence, or contact; for if this albuminoid substance 

 foe precipitated by alcohol, collected on a filter, and re- dissolved in 

 "water, it will still effect the transformation very rapidly, and will con- 

 vert 2000 times its own weight of starch into sugar. Neither dilute 

 alcohol or acids, nor, it is said, even a boiling heat, arrest altogether 

 the action of salivin. Finally, although the action of saliva is more 

 rapid and complete on cooked starch, yet grains of raw starch, masti- 

 cated and mixed with saliva in the mouth, and then maintained at a 

 temperature of 100, at length break down, and are converted into 

 sugar. The saliva has no specific action on gum, pectin, cellulose, or 

 fatty matters, unless it may, to a slight degree, emulsify the latter, 

 <nor yet on albuminoid or gelatinoid substances. 



