FOOD AND DIGESTION 



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 glucose (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 = (C 12 H 20 O 10 ) 10 -f-8H 2 O, which is further con- 

 verted by the ferment into 



i. Erythro-dextrin, (C 12 H 20 O 10 ) 9 (giving red with iodine) + 



Maltose (C 12 H 22 O n ). 

 then into 2. Erythro-dextrin (C 12 H 20 Oj ) 8 (giving yellow with iodine) 



+ Maltose 2 (C 12 H 22 O n ). 



next into 3. Achroo-dextrin (C 12 H 20 O 10 ) 7 + Maltose 3 (C 12 H 22 O n ). 

 And so on; the resultant being: 



Soluble starch (C 12 H 20 O 10 ) 10 + Water 8H 2 O = Maltose 8(C 12 H 22 O U ) + 

 Achroo-dextrin (C 12 H 20 O 10 ) 2 . 



Many observers, however, believe that the maltose simultaneously pres- 

 ent with ery thro- 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 

 hydrolysis in other starch molecules. They point out that in such a chemical 

 reaction of considerable time duration, it is improbable that all the starch 

 molecules 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- 

 oxide 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 facili- 

 tates 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 

 very faintly alkaline medium and is inhibited by strong alkalies and espe- 

 cially by acids even as weak as the acidity of the gastric juice. This last is 

 of particular importance since it raises the question as to how long the 

 ptyalin may act. 



