340 HANDBOOK OF PHYSIOLOGY. 



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

 One molecule of gelatinous starch is converted by the action of an amylolytic fer- 

 ment into n molecules of soluble starch. 



One molecule of soluble starch = 10 (Ci 2 H 20 O ]0 ) + 8 (H 2 O), which is further con- 

 verted by the ferment into 



1. Erythro-dextrin (giving red with iodine) -f Maltose. 



9 (C 12 H 20 O 10 ) (C, a H aa O n ) 



then into 2. Erythro-dextrin (giving yellow with iodine) -f- Maltose. 



8(C 12 H 20 10 ) 2 (C, a H aa On) 



next into 3. Achroo-dextrin Maltose. 



7(C, a H 20 Oio) 3(C ia H 22 On) 



And so on; the resultant being: 



10 (C 12 H 20 O 10 ) + 8 (H 9 O) = 8 (CiH,,Ou) -f 2 (C 12 H 20 O lo ) 

 Soluble starch Water Maltose Achroo-dextrin. 



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

 ent with erythro-dextrin is actually split off from the starch molecule in 

 the formation of erythro-dextrin ; they claim that it is rather the product 

 of more advanced hydrolysis in other starch molecules, and 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 a 

 series of more and more simple dextrins are formed which give rise finally 

 to the disaccharides. 



Test for Sugar. In such an experiment the presence of sugar 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 suboxide indicates the presence of sugar. 



The action of saliva, on starch is facilitated by : (a) Moderate heat, 

 about 37.8 C. (100 F.). (b) A neutral medium, (r) Eemoval of the 

 changed material from time to time. Its' action is retarded bt/ : (a) Cold; 

 a temperature ofO C. (32 F.) stops it for a time, but does not destroy it, 

 whereas a high temperature above 60 C. (140 F.) destroys it. (b) Acids 

 or strong alkalies either delay or stop the action altogether; the action 

 in a faintly alkaline medium is nearly as vigorous as in a neutral medium . 

 (c) Presence of too great a percentage of the changed material. Ptyalin, 

 in that it converts starch into sugar, is an amylolytic or diastasic ferment. 



Starch appears to be the only principle of food upon which saliva acts 

 chemically : the secretion has no apparent influence on any of the other 

 ternary principles, such as sugar, gum, cellulose, or on fat, and seems to 

 be equally destitute of power over albuminous and gelatinous substances. 



Saliva from the parotid is less viscid ; less alkaline, the first few drops 

 discharged in secretion being even acid in reaction ; clearer, although it 

 may become cloudy on standing from the precipitation of calcium carbon- 

 ate from escape of carbon dioxide ; and more watery than that from the 

 submaxillary. It has moreover a less powerful action on starch. Sub- 

 lingual saliva, is the most viscid, and contains more solids than either of 

 the other two, but has little diastasic action. 



