316 ACTION OF SALIVA. .BOOK n. 



with Fehling's fluid, shewing that maltose or dextrose is present. 

 That is to say the saliva has converted the starch into maltose 

 or dextrose. The presence of the previously absent sugar may 

 also be shewn by fermentation and by the other tests for sugar 

 Moreover, if an adequately large quantity of starch be subjected 

 to the charge, the sugar formed may be isolated, and its charac- 

 ters determined. When this is done it is found that while some 

 dextrose is formed the greater part of the sugar which appears is 

 in the form of maltose. As is well known, starch may by the 

 action of dilute acid be converted into dextrin, and by further 

 action into sugar ; but the sugar thus formed is always wholly 

 dextrose, and not maltose at all. The action of saliva in this 

 respect differs from the action of dilute acid. 



While the conversion of the starch by the saliva is going on 

 the addition of iodine frequently gives rise to a red or violet 

 colour instead of a pure blue, but when the conversion is complete 

 no coloration at all is observed. The appearance of this red 

 colour indicates the presence of dextrin (erythrodextrin) ; the 

 violet colour is due to the red being mixed with the blue of still 

 unchanged starch. 



The appearance of dextrin shews that the action of the saliva 

 on the starch is somewhat complex ; and this is still further 

 proved by the fact that even when the saliva has completed its 

 work the whole of the starch does not reappear as maltose or 

 dextrose. A considerable quantity of the other dextrin (achroo- 

 dextrin) always appears and remains unchanged to the end; and 

 there are probably several other bodies also formed out of the 

 starch, the relative proportions varying according to circumstances 

 The change therefore, though perhaps we may speak of it in a 

 general way as one of hydration, cannot be exhibited under a 

 simple formula, and we may rest content for the present with the 

 statement that starch when subjected to the action of saliva is 

 converted chiefly into the sugar known as maltose with a com- 

 paratively small quantity of dextrose and to some extent into 

 achroodextrin (erythrodextrin appearing temporarily only in the 

 process), other bodies on which we need not dwell being formed 

 at the same time. 



Raw unboiled starch undergoes a similar change but at a much 

 slower rate. This is due to the fact that in the curiously formed 

 starch grain the true starch, or granulose, is invested with coats 

 of cellulose. This latter material, which requires previous treat- 

 ment with sulphuric acid before it wi.ll give the blue reaction 

 on the addition of iodine, is apparently not acted upon by saliva. 

 Hence the saliva can only get at the granulose by traversing the 

 coats of cellulose, and the conversion of the former is thereby 

 much hindered and delayed. 



177. The conversion of starch into sugar, and this we may 

 speak of as the amylolytic action of saliva, will go on at the ordinary 



