1212 DEXTRINS. 



being the colour it yields with iodine. The violet observed 

 during the earlier stages of hydrolysis is due to an admixture of 

 the blue due to soluble starch with the red of the erythrodextrin. 



Commercial dextrin, which is very impure, containing dextrose 

 and frequently unaltered starch, usually yields a very strong red 

 coloration on the addition of iodine. 



(ii) Achroodextrin. When, during the prolonged enzymic 

 hydrolysis of starch under ordinary conditions, the addition of 

 iodine ceases to give any coloration, the fluid now contains 

 much sugar together with a considerable but variable propor- 

 tion of this dextrin, which has received its name from its 

 behaviour towards iodine, yielding no colour with this reagent. 

 It is the characteristic dextrin obtained during the prolonged 

 artificial digestion of starch with saliva (or pancreatic juice) 

 and may be separated from its solution by concentration and 

 the addition of an excess of alcohol. As thus prepared it is 

 mixed with much adherent maltose, from which it cannot be 

 entirely freed by washing with alcohol or by successive solution 

 in water and reprecipitation with alcohol. A partial separation 

 may be obtained by fermenting off the sugar with yeast or by 

 dialysis, since dextrin is non-diffusible. If however the mix- 

 ture be warmed with a slight excess of mercuric cyanide and 

 caustic soda, the whole of the sugar is destroyed in reducing 

 the mercuric salt, leaving in solution a non-reducing dextrin. 



Maltodextrin. This substance is described as appearing during 

 the earlier stages of a limited hydrolysis of starch-paste with dias- 

 tase, and it may perhaps similarly occur when saliva or pancreatic 

 juice is employed. It differs from the dextrins previously described 

 as follows. It is more soluble in alcohol and distinctly diffusible ; 

 it reduces Fehling's fluid, has a lower specific rotatory power and is 

 completely convertible into maltose by the further action of diastase. 

 It will therefore not be found among the products of a prolonged 

 hydrolytic degradation of starch. 



When starch-paste is hydrolyzed outside the body with 

 diastase or with animal enzymes some dextrin is always 

 obtained together with the sugars which make their charac- 

 teristic appearance during the process. There is however no 

 evidence that in the body any carbohydrate is absorbed as 

 dextrin from the alimentary canal. We shall therefore not be 

 far wrong in concluding that in the animal body starch is 

 completely converted into sugar previous to absorption, and 

 if this be the case the interest of the physiologist in the pri- 

 mary products of starch hydrolysis becomes very small, except 

 so far as a study of these products is essential to the elucida- 

 tion of the probable molecular magnitude and structure of the 

 parent-substance. 



