230 THE CARBOHYDRATES. 



MAQUENNE, mentioned above. According to him the amylose passes 

 directly into maltose without the formation of dextrin by the action of 

 malt infusion. The dextrins produced are only formed from the amylo- 

 pectin, which does not undergo saccharification with freshly prepared 

 malt infusions, but only with older or especially active infusions. This 

 also explains why in the older investigations the saccharification was 

 only about 80 per cent while MAQUENNE has been able to completely 

 convert the starch into sugar by enzymotic action. 



The various dextrins are very hard to isolate as chemical individuals 

 and to separate from each other. YOUNG 1 has tried their separation 

 by means of neutral salts, especially ammonium sulphate, and MOREAU 

 by the aid of a baryta-alcohol method. We cannot enter into the dif- 

 ferences as to the dextrins so separated, and only the characteristic 

 properties and reactions will be given for the dextrins in general. 



The dextrins appear as amorphous, white or yellowish-white powders 

 which are/ readily soluble in water. Their concentrated solutions are 

 viscid and sticky, like gum solutions. The dextrins are dextrogyrate. 

 They are insoluble or nearly so in alcohol, and insoluble in ether. Watery 

 solutions of dextrins are not precipitated by basic lead acetate. Dex- 

 trins dissolve cupric hydroxide in alkaline liquids, forming a beautiful 

 blue solution, which, as is generally admitted, is reduced by pure dex- 

 trins. According to MOREAU pure dextrin has no reducing action. The 

 dextrins are not directly fermentable. 



SCHARDINGER has discovered a bacillus which forms acetone from 

 starch and which is especially useful for the perparation of crystalline 

 cleavage products from starch. He obtained two crystalline substances, 

 dextrin a and 0, which are not fermentable by yeast and on hydrolysis 

 with acid yield glucose. For the a-dextrin PRINGSHEIM and LANGHANS 

 have determined the formula (CeHioC^ while BILTZ and TRUTHE 2 

 found the formula (CoHioCs^ for the /3-dextrin. 



The vegetable gums are soluble in water, forming solutions which are viscid 

 but may be filtered. We designate, on the contrary, as vegetable mucilages 

 those varieties of gum which do not or only partly dissolve in water, and which 

 swell up therein to a greater or less extent. The natural varieties of gum and 

 mucilage, to which belong several generally known and important substances, 

 such as gum arabic, wood-gum, cherry-gum, salep, and quince mucilage, and 

 probably also the little-studied pectin substances, will not be treated in detail, 

 because of their unimportance from a physiological standpoint. 



1 Journ. of Physiol., 22, which contains the older researches of Nasse, Kriiger 

 Neumeister, Pohl, and Halliburton. Moreau, 1. c. 



2 Schardinger, Centralbl. f. Bak. u. Parasitenkunde, II, 22, 98 (1909); 29, 118 (1911); 

 Pringsheim and Langhans, Ber. d. d. Chem. Gesellsch., 45, 2533 (1912); Biltz and 

 Truthe, ibid., 46, 1377 (1913). 



