312 FOOD AND DIGESTION 



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^H^O^) 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 maltose. Maltose is allied 

 to saccharose or cane-sugar more nearly than to glucose; it is crystalline; its 

 solution has the property of polarizing light to the right to a greater degree 

 than solutions of glucdse (3 to i); it is not so sweet, and reduces copper sul- 

 phate less easily. It can be converted into glucose by boiling with dilute 

 acids and by the action of the enzyme maltase present in saliva. 



According to Brown and Heron the reactions may be represented thus: 

 One molecule of gelatinous starch is converted by the action of an amylolytic ferment into 



n molecules of soluble starch. 



One molecule of soluble starch = io(Ci 2 H 2 oOio) + 8 (HaO), which is further converted 

 by the ferment into 



i. Ery thro -dextrin, 9(Ci2H2oOio) (giving red with iodine) -f- Mal- 

 tose (CiaHaaOn). 



then into 2. Erythro-dextrin 8 (CiaHaoOio) (giving yellow with iodine) -\- Mal- 

 tose 2 (Ci 2 H 22 O u ). 



next into 3. Achroo -dextrin 7 (Ci 2 H 20 Oio) + Maltose 3 (Ci 2 H 22 On). 

 And so on; the resultant being: 



Soluble starch 10 (Ci 2 H 20 Oio) + Water 8 (H a O) = Maltose 8 (CiaHaaOn) + 

 Achroo -dextrin 2 (Ci 2 H 2 oOio). 



Many observers, however, believe that the maltose simultaneously present 

 with erythro-dextrin is not actually split off from the starch molecule in the 

 formation of erythro-dextrin, but that it is the product of more advanced hydrol- 

 ysis in other starch molecules. They point out that in such a chemical re- 

 action of considerable time duration, it is improbable that all the starch mole- 

 cules are attacked at the same rate or are, at any given moment, equally 

 advanced in cleavage. Their theory is that there is a series of more and more 

 simple dextrins formed giving rise finally to the disaccharides. 



The presence of sugar in such an experiment is at once discovered by the 

 application of Trommer's test, which consists in the addition of a drop or 

 two of a solution of copper sulphate, followed by a larger quantity of caustic 

 potash. When the liquid is boiled, an orange-red precipitate of copper sub- 

 dxide indicates the presence of sugar. 



Influences which Affect the Action of Saliva on Starch. Moderate 

 heat, about 37.8 to 40 C, is most favorable to the rapid cleavage of starch 

 by the ptyalin. Cold retards and o C. suspends the action but does not de- 

 stroy the ferment. A temperature of 60 C. destroys the ptyalin. 



Removal of the products of salivary digestion as they are formed facilitates 

 the action of the enzyme, as an excess of these products is detrimental to further 

 action. 



The reaction between starch and saliva takes place best in a neutral or 



