in DIGESTION IN THE MOUTH AND STOMACH 157 



is sufficiently chewed in half a minute to determine the reflex of 

 deglutition, independent of the nature of the food. The masticated 

 pulp contains a certain quantity of coarse particles from 7-12 mm. 

 in diameter, according to the nature of the food ; the smallest 

 particles are only O'Ol mm. in diameter. Pieces larger than 

 12 mm. in diameter are retained in the mouth during deglutition 

 of the pulp; and subjected to fresh trituration. As a rule vegetable 

 foods are better masticated than animal matters. 



The most important function of saliva is certainly the prepara- 

 tion of a bolus from the masticated food, which is then ready for 

 deglutition. Saliva has no chemical action on the greater part of 

 the food-stuffs, and is limited to the conversion of the starch into 

 dextrin and sugar, with absorption of water. This action takes 

 place rapidly on cooked starch, very slowly upon raw, and is due 

 exclusively to the ptyalin, which acts in a slightly alkaline, or 

 even in a faintly acid medium, so that its action must cease in the 

 stomach, as soon as the acidity of the gastric juice exceeds that of 

 0'5 per cent HC1. The saccharifying power of the enzyme is less 

 when it is made to act on a large amount of starch ; moreover, it 

 is easily exhausted. 



Cannon and Day (1903) studied salivary digestion in the 

 stomach of the cat by isolating the different parts of the stomach 

 with ligatures, at a given time after the ingestion of food, and 

 testing them singly for the sugar content. They found that in 

 the fundus, the contents of which do not mix for a long time with 

 those of the pyloric region in the cat, the saliva produces a con- 

 spicuous formation of sugar from the starch, without disturbance 

 by the hydrochloric acid of the gastric juice. 



The amylolytic or diastatic action of the saliva is accomplished 

 in stages, i.e. it passes through certain intermediate products. 

 The first stage of starch conversion is that of amidulin (Nasse) or 

 soluble starch, which turns blue with iodine like insoluble starch ; 

 amidulin is then transformed into erythrodextrin (Briicke), which 

 turns deep red with iodine ; the erythrodextrin changes into 

 achroodextrin (Briicke), which no longer stains with iodine ; lastly, 

 a portion of the achroodextrin is converted into maltose (von 

 Mering and Musculus), and a small portion into glucose 

 (Zimmermann), which give the ordinary sugar reactions. 



Besides maltose, there is always a certain amount of dextrin 

 and unaltered starch in the end-products of the amylolytic action 

 of saliva, as exerted by ptyalin on starch. According to Sheridan 

 Lea, 3 '41 2 grms. of boiled starch, left to digest for a number of 

 hours with 100 c.c. of saliva, yield 2'83S grms. of maltose, and 

 0'505 grin, of dextrin. On the other hand, it is certain that a 

 small quantity of saliva suffices to saccharify a large amount of 

 starch (Briicke). 



Clemm (1902) showed that simple salivary digestion con- 



