INSALIVATION. 183 



achroodextrin with maltose, and the dextrin finally becomes mal- 

 tose, so that in the end all the starch becomes maltose. It is con- 

 sidered by some authorities that what is called erythrodextrin 

 consists in reality of several dextrins, and this is undoubtedly 

 true of achroodextrin, of which maltodextrin may be regarded as 

 a variety. Neumeister gives the following scheme as representing 

 the changes through which he believes the starch passes : 



(Maltose. 

 /Maltose. 

 Erythrodextrin. | /Maltose 



Achroodextrin a. 4 /Maltose. 



Achroodextrin /3. 4 



/Maltose. 



Achroodextrin y f 

 (maltodextrin). *) 



\Maltose. 



Glycogen, when acted upon by ptyalin, undergoes the same 

 changes as starch, but less rapidly. Cellulose is not affected by it, 

 except, possibly, in young plants, when it is very tender. Inas- 

 much as the external portion of the starch grains is cellulose, un- 

 cooked starch is not affected by this enzyme. This is one of the 

 reasons why starchy substances should be cooked before being 

 eaten. In the cooking process the starch becomes hydra ted by 

 union with water, and upon hydrated starch ptyalin acts more 

 thoroughly. 



Effect of Reaction on the Amylolytic Action of Saliva. The 

 saliva, of which ptyalin is a constituent, is an alkaline fluid, and 

 yet, as a matter of fact, this enzyme acts at its best when the 

 reaction is neutral. If the alkalinity is excessive, its action is 

 inhibited. When free hydrochloric acid is present, even in so 

 small an amount as 0.003 per cent., the amylolytic action is 

 arrested, and if much more than this, the enzyme is destroyed. 



From the experiments of Chittenden and Richards, to which 

 we have already referred, the following conclusions are drawn by 

 them: Saliva secreted after a period of glandular inactivity as 

 before breakfast, manifests greater amylolytic power than the 

 secretion obtained after eating. This increased amylolysis is due 

 primarily to an increase in the amount of active enzyme contained 

 in the saliva. Mixed saliva, whether collected by mechanical 

 stimulation or collected without effort, shows a natural tendency 

 to vary in amylolytic power throughout the twenty-four hours, and 

 apparently independently of the taking of food. This is remarkably 

 constant 'between 7 and 11 A.M. Mechanical stimulation, as 

 chewing a tasteless substance, and alcohol, ether, gin, whiskey, etc., 

 if taken into the mouth, all lead to the outpouring of a secretion 



