SALIVA AND SALIVARY DIGESTION. 75 



if we wish to neutralize, this must of course be done before 

 the volume is diluted to 100 cc.). The rotation will be found 

 to have very materially decreased ; it amounts to only about 

 one-third of the former rotation; in the case given to about 

 2.6 per cent. The decrease in the rotation is due to the trans- 

 formation by boiling with acids of the very strongly dextro- 

 rotatory dextrin (and maltose) into the less strongly rotating 

 glucose. 



(b) The alcoholic solution, when evaporated on the water- 

 bath, yields a very sweet-tasting sirup, which gradually 

 dries up, containing maltose with a little dextrin and a very 

 small quantity of glucose. The maltose crystallizes out of 

 this sirup only with great difficulty. It crystallizes more 

 readily if the digestion of the starch paste with the saliva be 

 continued for a longer time (twenty-four hours). On heat- 

 ing with acids the maltose, like the dextrin, yields glucose. 

 This conversion may be shown as in the case of dextrin by 

 the decrease in rotation. For this purpose dissolve 3 g. 

 of the residue in hot water, let cool, dilute to 150 cc., deter- 

 mine the rotation of the solution, then treat 100 cc. of this 

 solution just as in the case of dextrin, and determine the rota- 

 tion once more. It amounts to not quite half as much as 

 before boiling with the acid. 



Maltose, C 12 H 22 O n + H 2 0, is formed together with dextrin 

 by the action of malt (germinated barley) on starch by virtue 

 of a ferment (diastase) contained in the malt. Maltose crys- 

 tallizes in fine needles, it is strongly dextrorotatory (specific 

 rotation 139.2), reduces Fehling's solution, is fermentable, 1 

 :and is found in beer. To show the perfect fermentability, 

 add to about 50 cc. of a 2 per cent, solution some yeast, let 

 stand twenty-four hours at about 35, filter, and test the fil- 

 trate for sugar by means of Trommer's test: no precipitate 

 of cuprous oxide is formed. 



1 According to E. Fischer, maltose is first converted into glucose by 

 the maltase of the yeast and this then ferments. O. 



