CHEMICAL BASIS OF THE ANIMAL BODY. 1211 



a gelatinous residue on the filter, however dilute the starch- 

 paste may be which is used for the filtration. When subjected 

 to hydrolytic agencies such as superheated water, dilute acids 

 and enzymes the starch passes rapidly into true solution, yielding 

 at the same time a series of successive products to be described 

 below. 



2. Soluble starch (Amylodextrin) (C 6 H 10 O 5 )„. 



When starch-paste, heated to 40° C. on a water-bath, is 

 digested with a small amount of saliva and the whole stirred 

 so as to effect a thorough mixture of the two, the paste rapidly 

 loses its opalescent appearance, becoming limpid and clear like 

 water : the moment this change has taken place the digesting 

 mixture should be boiled to cut short the further action of the 

 ptyalin. The fluid thus obtained contains the first product of 

 the hydrolysis of starch to which the name of ' soluble starch ' 

 has been given. Its solution filters readily, and the filtrate 

 yields with iodine the pure blue characteristic of the original 

 unaltered starch. On the addition of an excess of alcohol the 

 soluble starch is precipitated, the precipitate after drying being 

 but little soluble in cold water, although it readily dissolves in 

 water at 60 — 70° C. It also yields a characteristic precipitate 

 with tannic acid, and differs in this respect from the dextrins. 

 It is dextrorotatory and does not reduce Fehling's fluid. The 

 same substance may be similarly obtained by the limited action 

 of malt-extract or pancreatic juice. 



3. The dextrins (C 6 H 10 O 5 ) n . 



When the hydrolytic action of saliva, malt-extract, or pan- 

 creatic 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 proper- 

 ties of the successively formed dextrins rendering their sepa- 

 ration and characterization extremely difficult. They are all 

 precipitable by alcohol, and differ from soluble starch in yield- 

 ing 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 ery- 

 throdextrin, whence the name. But little is definitely known 

 of this dextrin as a chemical individual, its chief characteristic 



