CHAP. I.] ACTION OF SALIVA UPON STARCH. 39 



The pure There can be no doubt, however, that neither by 



diastatic fer r Mialhe's nor by Cohnheim's method is it possible to 

 ment yet un- obtain the pure' salivary ferment. In this case as in 

 that of all other unformed ferments, our methods 

 merely enable the experimenter to obtain substances or extracts which 

 possess in an intense degree the activity of the glands or juices which 

 yield them. 



Brief outline of the Changes which Starch undergoes under the 

 influence of the Salivary Ferment 



When saliva acts upon unboiled starch grains, it exerts for a long 

 time no action upon it ; in order to insure any conversion of the 

 unboiled starch contact must be prolonged for days. The changes 

 which occur when saliva acts upon boiled starch have, by the 

 researches of Musculus and v. Mehring and of H. T. Brown, been 

 shewn to be similar to, and apparently identical with, those which 

 diastase produces. 



Preparation I n investigating the action of saliva or any other 



of a suitable iiq u id w hich contains a diastatic ferment it is conve- 

 starch-paste nient to be provided with a well-made starch-paste, 

 for experimen- This is best made 1 by using pure potato-starch. The 

 tai purposes. potato-starch is well washed with water, and treated 

 successively with a very dilute solution of potassic hydrate and a 

 1 per cent, solution of hydrochloric acid ; it is then washed with 

 water until the last trace of acid has disappeared and dried at 25C. 

 A portion of this starch is thoroughly mixed in a mortar with cold 

 water, and the thick liquid then poured with constant and rapid 

 stirring into boiling water and the process of boiling continued for 

 two or three minutes. 



The most suitable quantity of starch to be used per 100 c.c. is, accord- 

 ing to Brown and Heron, from 3 to 5 grammes, according to Dr Roberts, 

 1 gramme. The standard starch mucilage used in the process of ' diastasi- 

 nietry ' of this author is of the latter strength. 



Conversion of Gelatinous into Soluble Starch (Amylodextriri). 



The first step in the action of the ferment upon gelatinous starch 

 consists in the conversion of the latter into soluble starch, an action 

 which is accompanied by the liquefaction of the paste. 



This liquefaction takes place, at a suitable temperature, with 

 extreme rapidity (almost instantaneously), providing the quantity of 

 ferment be sufficient. 



The soluble starch, which is the first product of the action of 

 diastatic ferments, is, like insoluble starch, coloured blue by iodine. 



1 Brown and Heron. Op. ctt., note 1, p. 601. 



