CHEMICAL BASIS OF THE ANIMAL BODY. 93 



similarly obtained by the limited action of malt-extract or pancreatic 

 juice. 



3. The dextrins (CgH^Og)/. 



When the liydrolytic action of saliva, malt-extract, or pancreatic 

 juice on starch-paste is prolonged, the first-formed soluble-starch is 

 rapidly changed into a number of successive substances to which the 

 general name of dextrin is given. These products are intermediate 

 between soluble-starch and the sugars which result from the complete 

 hydrolysis of starch, and are probably very numerous, the similarity in 

 the properties of the successively formed dextrins rendering their 

 separation and characterisation extremely difficult. They are all 

 precipitable by alcohol, and differ from soluble-starch in yielding no 

 precipitate with tannic acid. 



(i) Erythrodextrin. If during the earlier stages of the hydrolysis 

 of starch-paste, successive portions of the solution be tested by the 

 addition of iodine, it may be observed that the pure blue which it 

 yields at first passes gradually through violet, and reddish- violet to 

 reddish-brown, the latter colour being supposedly due to the presence 

 in the solution of erythrodextrin, whence the name. But little is 

 definitely known of this dextrin as a chemical individual, its chief 

 characteristic being the colour it yields with iodine 2 . 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 colouration on the addition of 

 iodine. 



(ii) Achroodextrin 3 . When, during the prolonged enzymic hydro- 

 lysis of starch under ordinary conditions, the addition of iodine ceases 

 to give any colouration, the fluid now contains much sugar together 

 with a considerable but variable proportion 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 (see below), 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 



1 For the probable value of n in certain cases see Brown and Morris, cit. sub 

 starch. 



2 But see Musculus u. Meyer, Zt. physiol Chem. Bd. iv. (1880), S. 451. 



3 Brown and Morris, JL Ch. Soc. Vol. XLVII. (1885), p. 551. 



