CHEMISTRY OF DIGESTION AND NUTRITION. 285 



may be complete, and that the final product of their action may be maltose 

 alone. It will be found that this statement applies practically not to the 

 ptyalin, but to the similar amylolytic enzyme in the pancreatic secretion, owing 

 to the fact that, normally, food is held in the mouth for a short time only, and 

 that ptyalin digestion is soon interrupted after the food reaches the stomach. 

 With reference to the intermediate stages or products in the conversion of 

 starch to sugar it is difficult to give a perfectly clear account. It was formerly 

 thought that the starch was first converted to dextrin, and this in turn was 

 converted to sugar. It is now believed that the starch molecule, which is quite 

 complex, consisting of some multiple of C 6 H 10 O 5 — possibly (C 6 H 10 O 5 ) 20 — first 

 takes up water, thereby becoming soluble (soluble starch, amylodextrin), and 

 then splits, with the formation of dextrin and maltose, and that the dextrin 

 again undergoes the same hydrolytic process, with the formation of a second 

 dextrin and more maltose; this process may continue under favorable con- 

 ditions until only maltose is present. The difficulty at present is in isolating 

 the different forms of dextrin that are produced. It is usually said that at 

 least two forms occur, one of which gives a red color with iodine, and is there- 

 fore known as erythrodextrin, while the other gives no color reaction with 

 iodine, and is termed achroodextrin. It is pretty certain, however, that there 

 are several forms of achroodextrin, and, according to some observers, erythro- 

 dextrin also is really a mixture of dextrins with maltose in varying propor- 

 tions. In accordance with the general outline of the process given above, 

 Neumeister 1 proposes the following schema, which is useful because it gives a 

 clear representation of one theory, but which must not be considered as satis- 

 factorily demonstrated (see also the section on Chemistry of the Body). 



r Maltose. 

 /Maltose. 



Erythrodextrin. < 



/Maltose. 



Achroodextrin a. < 



/Maltose. 



Achroodextrin /3. / 



/Maltose. 



Achroodextrin y ( 

 (maltodextrin). ""» 



\Maltose. 



This schema represents the possibility of an ultimate conversion of all the 

 starch into maltose, and it shows at the same time that maltose may be pres- 

 ent very early in the reaction, and that it may occur together with one or more 

 dextrins, according to the stage of the digestion. It should be said in conclu- 

 sion that this description of the manner of action of the ptyalin is supposed to 

 apply equally well to the amylolytic enzyme of the pancreatic secretion, the 

 two being, so far as known, identical in their properties. From the stand- 

 point of relative physiological importance the description of the details of 

 amylolytic digestion should have been left until the functions of the pancre- 

 atic juice were considered. It is introduced here because, in the Datura! order 

 1 Lehrburh der physiologiscken Chemie, 1893, p. 232. 



