THE SALIVA. Ill 



starch to sugar. This can be readily demonstrated as follows : A few 

 cubic centimeters of saliva are added to a small amount of starch solu- 

 tion and kept at a temperature of about 35 C. If a drop of this mixt- 

 ure is then tested at intervals of about one minute with a dilute solu- 

 tion of iodine, it will be observed that the blue color, which is first 

 obtained by bringing a drop of the two solutions together, soon gives 

 place to a violet, and then to a mahogany brown, and that still 

 later no color-reaction whatever occurs. As soon as this point is 

 reached a small amount of the starch mixture is examined with 

 Trommer's or Fehling's solution (see page 278), when the presence 

 of sugar can be established. The sugar which thus results is maltose, 

 Avhile the intermediary products which are formed during the inver- 

 sion of the starch are represented by erythrodextrin, achroodextrin, 

 -and isomaltose. The reaction which takes place may be represented 

 by the equations : 



(1) (C I2 H M 10 ) M + 3H 2 = 3[(C 12 H 20 10 ) 17 .C 12 H 22 O n ] 



Amidulin. Erythrodextrin. 



<2) 3[(C I2 H ao O IO ) I7 .C u H a O I1 ] + 6H 2 = 9[(C 12 H 20 O 10 ) 5 .C 12 H 22 O n ] 



Achroodextrin. 



(3) 9[(C 12 H 20 10 ) 5 .C 12 H 22 U ] + 45H 2 = 54C 12 H 22 O U = 54C 12 H 22 O M 



Isomaltose. Maltose. 



We shall return to these reactions in the next chapter, when the 

 digestion of the food is considered in detail. 



To isolate the ptyalin from saliva, the following method, which 

 has been suggested by Gautier, may be employed : To a large 

 quantity of saliva 98 per cent, alcohol is added so long as a floccu- 

 lent precipitate is seen to form. This is collected on a small filter 

 and dissolved with a small amount of distilled water. The solu- 

 tion is treated with a few drops of a solution of bichloride of mercury, 

 in order to remove any albuminous material that may be present. 

 In the filtrate the excess of the bichloride is removed with hydrogen 

 .sulphide, when the remaining liquid is evaporated to dryness at a 

 temperature not exceeding 40 C., and the residue is treated with 

 strong alcohol. The insoluble portion is then dissolved with a small 

 amount of distilled water, filtered, dialyzed in order to remove inor- 

 ganic salts, and finally precipitated with absolute alcohol, when the 

 ptyalin will separate" out in light flakes. Obtained in this manner, 

 ptyalin is a white amorphous substance, which is soluble in water, 

 dilute alcohol, and glycerin. In neutral or slightly alkaline solu- 

 tion, but not in acid solution, it rapidly transforms boiled starch 

 into sugar at a temperature of from 36 to 40 C. Heated to a 

 temperature of 60 C., its solutions lose this power, and it is thus 

 possible to distinguish between ptyalin and the diastatic ferment of 

 vegetable origin, for which the optimum temperature lies between 

 60 and 65 C. 



Of special interest is the fact that the transformation of starch 

 into sugar ceases as soon as the latter is present to the extent of 

 from 2 to 2.5 per cent. This phenomenon is common to all enzy- 



