PHYSIOLOGICAL ACTIONS OF THE SALIVA. 265 



io(C 12 H 20 10 ) + 8(H 2 0) = 8(C 12 H 22 U ) + 2 (C 12 H 20 O 10 ) 



Starch + Water = Maltose + Dextrin. 



The exact course of events is as follows: At first with liquefaction of the 

 starch-paste amylodextrin is formed. This does not reduce Fehling's solution; it is 

 colored blue by iodin and is the principal constituent of the preparation formerly 

 called soluble starch or amydulin. It is transformed into three molecules of 

 erythrodextrin, which reduces Fehling's solution feebly, and is colored red by 

 iodin. The erythrodextrin is transformed into three molecules of achroodextrin, 

 which reduces Fehling's solution, but is not stained by iodin. From this iso- 

 maltose and maltose are formed, the latter being formed from the former by the 

 action of ptyalin. Isomaltose undergoes fermentation with greater difficulty 

 than maltose. Finally all the starch is changed into maltose and dextrose. 



When little ferment is present and the action is of short duration, the saliva or 

 the pancreatic juice produces isomaltose principally; when much ferment is pres- 

 ent and the action is of longer duration, the formation of maltose and of some 

 dextrose is favored. The maltose subsequently may be changed in the intestine 

 into dextrose, but the greater part is absorbed unchanged. 



Kirchof, in 1811, showed that dextrose is formed from starch, by boiling 

 with dilute sulphuric or hydrochloric acid. 



Demonstration of Ptyalin. This depends, as in the case of all hydrolytic fer- 

 ments, upon the fact that a voluminous precipitate formed in the saliva carries the 



FIG. 96. Potato Starch. 



ferment down with it mechanically, and from it the latter is then isolated by simple 

 means. For this purpose the saliva is strongly acidulated with phosphoric acic 

 lime-water is added until the reaction is rendered alkaline. As a res 

 precipitate of basic calcium phosphate forms, carrying the ptyalin down w 

 This precipitate is collected upon a filter and the ptyalin is dissolved out 

 the aid of a little water. Alcohol precipitates the ptyalm in this watery e 

 as a white powder. By repeated solution in water, and subsequent precipitatic 

 with alcohol, the ptyalin is obtained in an absolutely pure 



The cells of the glands first contain ptyalin in a preliminary stage 

 a ptyalinogenic substance, from which ptyalin is formed only during . * 

 Ptyalin contains nitrogen, is free from ash, but yields no xanthoproteic react 

 It is precipitated from solution by neutral or basic lead acetate. 



deC T P Wi?t S ich y taS "ptval- could be extracted with glycerin containing 

 water from the salivary glands of human beings or swine, cleansed, minced, 



