FOOD AND DIGESTION. 339 



completely converted into a paste or gruel, which is called gelatinous 

 starch. 



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

 hydrolysis) into soluble starch, or amidulin; this is more limpid and more 

 like a true solution, though it still gives the blue coloration on the addi- 

 tion of iodine. This stage is very brief, only thirty seconds being some- 

 times required in laboratory experiments, to render a stiff starch paste 

 completely fluid when a few drops of saliva are added at body temper- 

 ature. 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. 



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

 variable mixture of maltose and iso-maltose with dextrins, but never re- 

 sult (in laboratory experiments) in the complete conversion of the dex- 

 trins into sugars. Gradually, as the starch is converted, the blue color- 

 ation with iodine is replaced by a purplish-red and finally by a distinctly 

 red color : the latter color is produced by erythro-dextrin (so-called from 

 the color), a hypothetical substance which has never been isolated. 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-dex- 

 trin, 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 follows : 



Starch. 

 Soluble starch. 



Erythro-dextrin. Maltose and iso-maltose. 



Achroo-dextrins. Maltose and iso-maltose. 



The sugars formed are maltose (C ]2 H 2i! O n ) and a closely allied sugar 

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

 some observers, and this may be due to the action of glucase. Maltose is 

 allied to saccharose or cane-sugar more nearly 'than to glucose ; it is crys- 

 talline ; its solution has the property of polarizing light to the right to a 

 greater degree than solutions of glucose (3 to 1) ; it is not so sweet, and 

 reduces copper sulphate less easily. It can be converted into glucose by 

 boiling with dilute acids. 



