THE DIGESTION OF THE FOODSTUFFS 125 



forming ferment of sprouting barley) in that the former is most 

 active at 40, while the latter acts most energetically at 60. 



Ptyalin is a proteid-like body. It can be obtained for experi- 

 ments in digestion from fresh or dried salivary glands by extracting 

 the gland with water or glycerin. 



Ptyalin acts best in neutral solutions. It is rendered in- 

 active and is destroyed by alkalies and especially by mere 

 traces of free mineral acids. Organic acids only inhibit its 

 activity. Ptyalin is destroyed by temperatures above 60. 

 Maltose is the chief product in the digestion of starch by 

 ptyalin, only little dextrose being formed. According to 

 later researches, the small amount of grape-sugar is not 

 formed by the direct action of ptyalin upon starch, but is 

 formed from maltose by the activity of a second ferment, 

 glucase. Ptyalin itself forms maltose only. 



In this formation of maltose from starch, a number of in- 

 termediate products, called dextrins, are formed. These 

 dextrins differ from each other in their behavior towards 

 iodine and are called amylo-, erythro-, and achroo-dextrins, 

 according as they color blue or red or do not color with 

 iodine. 



The saliva of carnivorous animals contains no ptyalin; in this 

 case, the saliva only seems to moisten and lubricate the dry food. 

 Mammals living in the water and not eating dry food have no 

 salivary glands. 



Saliva also serves to moisten and clean the mouth. 



3. Deglutition. By deglutition or swallowing, the chewed 

 food is moved into the stomach. 



The bolus is moved from the anterior end of the tongue 

 along the hard palate to the anterior pillars of the fauces. 

 By the stimulation of the sensory nerves ending in the 

 mucous membrane at this part, a reflex action is produced 

 which results in a forcible contraction of the mylohyoid and 

 hyoglossal muscles. By this the bolus is pushed backward 

 into the esophagus. 



In order that food shall only escape backward, the pharyngeal 

 cavity must be separated from the mouth, nose, and larynx. This 

 is accomplished as follows: 



