236 HANDBOOK OF PHYSIOLOGY. 



gives no color with iodine. However long the reaction goes on, it is un- 

 likely that all the dextrin becomes sugar. 



Next with regard to the kind of sugar formed, it is, at first at any 

 rate, not glucose but maltose, the formula for which is C^H.,,,0^ Mal- 

 tose is allied to saccharose or cane-sugar more nearly than to glucose ; it 

 is crystalline ; its solution lias the property of polarizing light to a 

 greater degree than solutions of glucose ; is not so sweet, and reduces 

 copper sulphate le'ss easily. It can be converted into glucose by boiling 

 with dilute acids, and by the further action of the ferment. 



According to Brown and Heron the reactions may be represented 

 thus : 

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



lolytic ferment into n molecules of soluble starch. 



One molecule of soluble starch = 10 (C 12 H 20 10 ) 4- 8 (H a O), which is 

 further converted by the ferment into 



1. Erythro-dextrin (giving red with iodine) 4- Maltose. 



MC.A.O,.) (0,^,0,,) 



then into 2. Erythro-dextrin (giving yellow with iodine) 4- Maltose. 



8'(0,.H 1 .0 I .) 

 next into 3. Achroo-dextrin 4- Maltose. 



7 (O l ,H M O l .) 3 (C la H S2 O u ) 



And so on ; the resultant being : 



10 (C,,H !0 OJ + 8 (H,0) = 8 (0,.H M 11 ) + 2 .,. 

 Soluble starch Water Maltose Achroo-dextrm. 



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 100 F. (37.8 0.). (b) A slightly alkaline medium, (c) Kemoval 

 of the changed material from time to time. Its action is retarded ~by (a) 

 Cold ; a temperature of 32 F. (0 C.) stops it for a time, but does not 

 destroy it, whereas a high temperature above 140 F. (60 C.) destroys it. 



(b) Acids or strong alkalies either delay or stop the action altogether. 



(c) Presence of too much of the changed material. Ptyalin, in that it 

 converts starch into sugar, is an amylolytic 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 alkine, clearer, and more 

 watery than that from the submaxillary. It has moreover a less power- 

 ful action on starch. Sublingual saliva is the most viscid, and contains 



