THE Ml 'H INISMS 01 DIQ1 SI [( 1 1". 



starchy food is little chewed, the Length of time required for the mastica- 

 tion of other foods depending mainly on their nature, but also to a 

 certain degree on the appetite and on the size of the mouthful. 



It can not be too strongly insisted upon thai the mastication is 



of far more importance than merely t<> break up and pi 

 for swallowing. It causes the food to I"' moved about in the moutl 

 to develop its full effed on the last.' buds; the crushing 

 odors which stimulate the olfactory epithelium, On tl timuli dep< 



the satisfaction and pleasure of eating, which in turn initiate 

 of gastric digestion see page 135 . 



The benefit to digestion as a whole of a large secretion of saliva, brought 

 about by persistenl chewing, has been assumed by some to be much 

 greater than it really is, and there has existed, and indeed may still 

 exist, a school of faddists who, by deliberately chewing far beyond 

 the necessary time, imagine themselves to thrive better on 1< '1 than 



those who occupy their time with more profitable pursuits. 



Deglutition or Swallowing 

 After being masticated tho fond is polled up into a bolus by the action 



of the tongue againsl the palate, and after being lubricated by saliva is 



moved, by elevation of the front of the tongue, towards the back of the 

 mouth. This constitutes the first stag< of swallowing, and far, a 



voluntary act. About this time a slight inspiratory contraction of the 

 diaphragm occurs — the so-called respiration of swallowing a 

 mylohyoid quickly contracts, with the consequence that the bolus pat 

 between the pillars of the fauces. This marks the beginning of the 

 second stage, the first event of which is that the bolus, by stimulating 

 sensory nerve endings, acts on nerve centers situated in the medulla 



oblongata bo as to cause a i rdinated seri< movemei I 



muscles of the pharynx and larynx and an inhibition for a moment 

 the respiratory center paj 

 The movements alter the shape of the pharynx and of the varii 

 nings into ii in such a manner i the bolus 



into the esophagus Fig. 153 thus, I) th< palate b< 



elevated and the posterior wall of the pharynx bulges forr 

 shut off the posterior nares, 2 the posterior pillars 

 proximate so as to shut on* the mouth cavit: 



a second after the mylohyoid ; ted, the laryi : up- 



wards and forwards under the root of the toi nrhich 



drawn backwards becomes bai ked up 'he la- Phis 



pulling up <>f the larynx brings the opening int. 

 half of the dorsal side of the i piglottis, but the U] tl - -•rue- 



