POLYSACCHARIDS OR AMYLOSES. 97 



an enzyme ptyalin the action being one of hydrolysis. Pancreatic 

 juice produces the same change as does saliva ; and as the action 

 of saliva is due to the enzyme ptyalin, so is the action of pancreatic 

 juice due to an enzyme, amylopsin. 



Erythrodextrin. If the action of either of these enzymes upon 

 starch is not arrested in the soluble-starch stage, erythrodextrin 

 is formed. The blue color caused by the action of iodin on starch 

 gradually changes into violet, reddish violet, and then to reddish 

 brown as the starch gradually changes to erythrodextrin. This 

 reddish-brown color produced by iodin is the test for erythro- 

 dextrin. 



Achroodextrin. If the action of these enzymes is continued, 

 a still further change in the starch takes place. It passes into the 

 condition of achroodextrin, and iodin fails to produce any color. 

 A further change into maltose follows the formation of achroo- 

 dextrin. In the action of these enzymes upon starch outside the 

 body the first product is a mixture of dextrin with the sugar, but 

 within the body there is little doubt that all the starch is converted 

 into sugar, and as such is absorbed. If starch is treated with 

 boiling dilute acids instead of with these enzymes, the changes 

 just described take place with far greater rapidity, and dextrose 

 results. 



Maltodextrin. If diastase, the enzyme contained in malt 

 extract, is used instead of saliva or pancreatic juice, maltodextrin 

 is formed ; and indeed it is not certain that the latter substance is 

 not formed in addition to the erythrodextrin and achroodextrin 

 when saliva and pancreatic juice are employed. Maltodextrin 

 diifers from the dextrins already described in being more soluble 

 in alcohol, in being diffusible, and in responding to Fehling's test. 

 It also passes over into maltose by the continued action of the 

 diastase. 



Glycogen. The similarity between glycogen and starch has led 

 to the term "animal starch" being applied to the former. Glycogen 

 was first discovered in the liver, where it is normally found to the 

 amount of between 1.5 and 4 per cent, of the weight of the organ, 

 which may in man be increased to 10 per cent. It also exists in 

 muscles to the amount of from 0.5 to 0.9 per cent., and it is 

 estimated that all the muscles of the body contain as much glyco- 

 gen as does the liver. It occurs also in the integument and the 

 mucous membranes of the human embryo, in the placenta and 

 the amnion, in white blood-corpuscles and in pus-corpuscles, in 

 oysters and in other mollusca. For purposes of study it is usu- 

 ally obtained from the liver of an animal (a rabbit or a dog), in 

 which it is stored up in amorphous granules around the nuclei of 

 the liver-cells. Glycogen is soluble in water, and with iodin gives 

 a port-wine color. This color does not distinguish it from erythro- 

 dextrin ; but when it exists pure, as ordinarily it does not, it is 

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