356 FOOD AND DIGESTION 



velope of cellulose, which does not give a blue color with iodine except on 

 addition of sulphuric acid, and of granulose, which is contained within, and 

 which gives a blue color with iodine alone. Briicke states that a third body 

 is contained in the granule, which gives a red color with iodine, viz., erythro- 

 granulose. The granulose swells up on boiling, bursts the envelope, and the 

 whole granule is more or less completely converted into a paste or gruel 

 which is called gelatinous starch. 



When ptyalin acts upon boiled starch, it first changes the latter, by hydrol- 

 ysis, into soluble starch, or amidulin; this is more limpid and more like a true 

 solution, though it still gives the blue coloration on the addition of iodine. 

 This stage is very brief, only thirty seconds being sometimes required in labo- 

 ratory experiments to render a stiff starch paste completely fluid when a few 

 drops of saliva are added at body temperature. This rapidity of action is of 

 great importance, as under proper conditions of mastication practically all 

 the boiled starch of the food ought to enter the stomach as soluble starch. 

 When the starch has not been previously boiled, the envelope of cellulose 

 retards the action of the ptyalin to a very marked degree. 



Starch. 

 Soluble starch. 



Erythro-dextrin. Maltose and iso-maltose. 



Achroo-dextrins. Maltose and iso-maltose. 



The further stages of hydrolytic cleavage result in the formation of a 

 variable mixture of maltose and iso-maltose with a series of dextrins, but ap- 

 parently never result (in laboratory experiments) in the complete conversion 

 of the dextrins into sugars. Gradually, as the starch is converted, the blue 

 coloration with iodine is replaced by a purplish-red and finally by a red 

 color: the latter color is produced by ery thro- dextrin (so called from the 

 color). In the later stages no coloration is obtained with iodine, and for this 

 reason the dextrins formed are known as achroo- dextrins', there are probably 

 several of these, but they have not yet been sufficiently isolated. As sugar 

 appears very early in the process, even at the stage of erythro-dextrin, and 

 gradually increases in amount, it is generally concluded that maltose is 

 formed early in the decomposition of the starch molecule. The process is 

 usually represented schematically as above. 



The sugars formed are maltose (C 12 H 22 O n ) and a closely allied sugar 

 known as iso-maltose. A small percentage of dextrose has been found by 

 some observers, and this is due to the action of maltase. Maltose is allied 



