FUNCTION OF SALIVA 311 



Certain investigators have of late asserted that saliva contains another enzyme, 

 known as maltase, which has the power of splitting the disaccharides into 

 monosaccharides, or maltose into dextrose. The action of this ferment is 

 certainly very limited. The conversion of the starch under the influence of the 

 ferment into sugar takes place in several stages, and in order to understand 

 it a knowledge of the structure and composition of starch granules is neces- 

 sary. A starch granule consists of two parts: an envelope of cellulose, which 

 does not give a blue color with iodine except on addition of sulphuric acid, 

 and of granulose, which is contained within, and which gives a blue color 

 with iodine alone. Briicke states that a third body is contained in the granule, 

 which gives a red color with iodine, viz., erythro-granulose. On boiling, the 

 granulose swells up, bursts the envelope, and the whole granule is more or 

 less completely converted into a paste or gruel, which is called gelatinous 

 starch. 



When ptyalin acts upon boiled starch, it first changes the latter, by hydro- 

 lysis, into soluble starch, or amidulin; this is more limpid and more like a true 

 solution, though it still gives the blue coloration on the addition of iodine. 

 This stage is very brief, only thirty seconds being sometimes required in labora- 

 tory experiments to render a stiff starch paste completely fluid when a few 

 drops of saliva are added at body temperature. This rapidity of action is of 

 great importance, as under proper conditiqns of mastication practically all 

 the boiled starch of the food ought to enter the stomach as soluble starch. 

 When the starch has not been previously boiled, the envelope of cellulose 

 retards the action of the ptyalin to a very marked degree. 



Starch. 



I 

 Soluble starch. 



Erythro-dextrin. Maltose and iso-maltose. 



I 



Achroo-dextrins. Maltose and iso-maltose. 



The further stages of hydrolytic cleavage result in the formation of a 

 variable mixture of maltose and iso-maltose with a series of dextrins, but ap- 

 parently never result (in laboratory experiments) in the complete conversion 

 of the dextrins into sugars. Gradually, as the starch is converted, the blue 

 coloration with iodine is replaced by a purplish-red and finally by a red 

 color: the latter color is produced by erythro-dextrin (so-called from the 

 color). In the later stages no coloration is obtained with iodine, and for this 

 reason the dextrins formed are known as achroo-dextrins; there are probably 

 several of these, but they have not yet been sufficiently isolated. As sugar 

 appears very early in the process, even at the stage of erythro-dextrin, and 



