ALIMENTATION. 1 83 



SALIVARY DIGESTION. 



For anatomical considerations, see Mouth. 



Saliva is alkaline in reaction, its specific gravity is 1004.5, and 

 its amount in 24 hours is 84 pounds. Its composition (Meade- 

 Smith, from Lassaigue) is as follows for mixed saliva — 



Water 992.00 



Mucus and albumin 2.00 



Carbonates i .08 



Chlorides 4.92 



Phosphates, etc traces. 



1000.00 



It also contains epithelium, mucin, pytalin, serum, albumin^ 

 globulin and sulpho-cyanide of potassium. 



The parotid saliva is the largest in amount and most watery. 



The sub-maxillary is viscid and contains no albumin, and the 

 sub-lingual is very viscid and contains a large amount of solids. 



Action of the Saliva. — It has a mechanical action, by lubricating 

 the bolus of food, and a chemical by the action of its ferment, 

 ptyalin. This converts starch into sugar, and cane sugar into grape 

 sugar. As this process takes several minutes, it continues going 

 on in the stomach. 



DEGLUTITION. 



The act of deglutition consists of the passage of the food from 

 the mouth to the stomach ; it is divided into three stages ; the 

 first stage comprises the passage of the bolus from the mouth 

 through the fauces to the pharynx ; the second, its passage through 

 the pharynx, and the third when it passes through the oesophagus. 



In the first stage, the tip, body and base of the tongue press 

 against the hard palate, and push the bolus along toward the 

 pharynx, the teeth being closed. The palato-glossi and pha7'yngei 

 then contract and force the bolus into the pharynx, the palatal 

 curtain being carried against the superior pharyngeal wall. 



In the second stage the constrictors contract, the epiglottis 

 closes the top of the larynx, and the bolus is passed into the 

 oesophagus. 



In the thi7-d stage the oesophagus contracts on the bolus, and 



