USES OF THE SALIVA 1/5 



Several carbohydrates are formed as intermediate products between 

 starch and sugar by the action of the salivary enzyme. These are not 

 thoroughly understood by physiological chemists for the reason that the 

 size of the different molecules has not been definitely ascertained. The 

 following, however, is perhaps the simplest explanation of these changes. 

 The formula for starch is (C 6 H 10 O 5 );z, the "n" indicating that the mole- 

 cule is represented by the formula multiplied by an unknown number 

 not less than five. This is changed into soluble starch, which forms a 

 clear solution in water, which filters readily and strikes a blue color with 

 iodin. Its formula is the same as for starch, but the molecule probably 

 is larger. Soluble starch is then converted into dextrin, which has the 

 same formula, but a smaller molecule. At least two kinds of dextrin 

 have been recognized ; one, erythrodextrin, strikes a red color with 

 iodin and is readily converted into maltose, while the other, achroodex- 

 trin, has no reaction with iodin and is slowly converted into maltose. 

 Leaving out of consideration the size of the molecules, 2 (C 6 H 10 O 5 ) + 

 H 2 O = C 12 H 22 O n , which is the formula for maltose. It is probable 

 that some of the starch acted on by the saliva passes into the stomach 

 in the condition of achroodextrin. A certain part, also, may be changed 

 into dextrose (C 6 H 12 O 6 ). A full discussion of these changes, however, 

 belongs to special treatises on physiological chemistry. 



The action of the saliva on starch is due entirely to the presence of 

 ptyalin, although its intensity is increased in moderately alkaline solu- 

 tions or by the addition of certain salts, especially sodium chloride. 

 Feeble acids diminish the activity of this change, and it is arrested by 

 strong mineral acids ; although direct experiments have shown that the 

 action of the saliva is slowly and feebly continued in the stomach. The 

 temperature at which the action of the salivary enzyme is most vigorous 

 is about 100 Fahr. (38 C); and any considerable variation from this 

 temperature arrests the process. 



In early infancy the action of the saliva on starch is not so vigorous 

 as in the adult; and it is said that immediately after birth the parotid prod- 

 uct is the only one of the salivary secretions that contains ptyalin. In 

 a few months, however, ptyalin appears in the submaxillary and sub- 

 lingual secretions. 



It is evident that the saliva, in addition to its mechanical action, 

 transforms a considerable part of starch into sugar; but it is by no 

 means the only secretion engaged in its digestion, similar properties 

 belonging to the pancreatic and the intestinal juices. The last-named 

 secretions are probably more active, even, than the saliva. The saliva 

 acts slowly and imperfectly on raw starch, which becomes hydrated in 

 the stomach and is digested mainly by the liquids of the small intestine. 



