PHYSIOLOGICAL ACTION OF SALIVA. 295 



gives a blue with iodine, but after it has been acted on for a time it 

 gives a red or violet colour, indicating the presence of erythrodextrin, 

 there being a simultaneous production of sugar; but ultimately no 

 colour is obtained on adding iodine achroodextrin, which gives no 

 colour with iodine, and maltose being formed. The presence of the 

 maltose is easily determined by testing with Fehling's solution. 



Brown and Heron suggest that the final result of the transformation 

 may be represented by the equation 



10 (C 12 H 20 10 ) + 8 H 2 = 8 (C 12 H 22 O n ) + 2 (C 12 H 20 10 ) 



Soluble starch. Water. Maltose. Achroodextrin.] 



The ferment slowly changes maltose into grape-sugar or dextrose. 

 This result may be brought about much more rapidly by boiling maltose 

 with dilute sulphuric or hydrochloric acid. Achroodextrin ultimately 

 passes into maltose, and this again into dextrose ; the other form of 

 dextrin does not seem to undergo this change (Seegen's Dystropodex- 

 trin). For the further changes that maltose undergoes in the intestine, 

 see Intestinal Juice, ii., 2. 



[The formula of starch is usually expressed as C 6 H 10 5 , but the researches 

 already mentioned, and those of Brown and Heron, make it probable that it is more 

 complex, which we may provisionally represent by n (C^HgoOjo).] 



According to Musculus and Meyer, erythrodextrin is a mixture of dextrin and 

 soluble starch. 



Preparation Of Ptyalin. (1.) Like all other hydrolytic ferments, it is carried 

 down with any copious precipitate that is produced in the fluid which contains it. 

 It is easily isolated from the precipitate. The saliva is acidulated with phos- 

 phoric acid, and lime-water is added until the reaction becomes alkaline, when a 

 precipitate of basic calcium phosphate occurs, which carries the ptyaline along with 

 it. This precipitate is collected on a filter and washed with water, which dissolves 

 the ptyaline, and from its watery solution it is precipitated by alcohol as a white 

 powder. It is redissolved in water and reprecipitated, and is obtained pure (Cohn- 

 heim). 



(2.) V. W'MlcKs method. The salivary glands [rat] are chopped up, placed in 

 absolute alcohol for twenty-four hours, taken out and dried, and afterwards 

 placed in glycerine for several days. The glycerine extracts the ptyalin. It is 

 precipitated by alcohol from the glycerine extract. 



(3.) William Roberts recommends the following solutions for extracting ferments 

 from organs which contain them: (1) A 3-4 p.c. solution of a mixture of two parts 

 of boracic acid and 1 part borax. (2) Water, with 12-15 p.c. of alcohol. (3) One 

 part chloroform to 200 of water. 



Diastatic action Of Saliva. (.) The diastatic or sugar-forming action is 

 known by: (1) The disappearance of the starch. When a small quantity of starch 

 is boiled with several hundred times its volume of water, starch mucilage is 

 obtained, which strikes a blue colour with iodine. If to a small quantity of this 

 starch a sufficient amount of saliva be added, and the mixture kept for some 

 time at the temperature of the body, the blue colour disappears. (2) The presence 

 of sugar is proved directly by using the tests for sugar ( 149). 



(&.) The action takes place more slowly in the cold than at the temperature of 



