DIGESTION. 23 



COMPARISON OF INGESTA AND EGESTA IN 24 HOURS. 



FOOD, DRINK, AIR. OZ. EXCRETIONS. OZ. 



- ..... 43.40 





Water (6 pints) 93-OO Urine 66.31 



Oxygen 26.24 Solid excreta 6.07 



Total 13940 Total 13940 



DIGESTION. 



Digestion is a physical and chemical process, by which the food intro- 

 duced into the alimentary canal is liquefied and its nutritive principles 

 transformed by the digestive fluids into new substances capable of being 

 absorbed into the blood. 



The Digestive Apparatus consists of the alimentary canal and its 

 appendages, viz. : teeth, salivary, gastric and intestinal glands, liver and 

 pancreas. 



Digestion may be divided into seven stages : prehension, mastication, 

 insalivation, deglutition, gastric and intestinal digestion and defecation. 



Prehension, the act of conveying food into the mouth, is accomplished 

 by the hands, lips and teeth. 



Mastication is the trituration of the food, and is accomplished by 

 the teeth and lower jaw, under the influence of muscular contraction. 

 When thoroughly divided, the food presents a greater surface for the 

 solvent action of the digestive fluids, thus aiding the general process of 

 digestion. 



The Teeth are thirty-two in number, sixteen in each jaw, and divided 

 into four incisors or cutting teeth, two canines, four bicuspids, and six 

 molars or grinding teeth; each tooth consists of a crown covered by 

 enamel, a neck, and a root surrounded by the crusta petrosa, and imbedded 

 in the alveolar process ; a section through a tooth shows that its substance 

 is made of dentine, in the centre of which is the pulp cavity, containing 

 blood vessels and nerves. 



The lower jaw is capable of making a downward and an upward, a 

 lateral and an antero-posterior movement, dependent upon the construction 

 of the temporo-maxillary articulation. 



The jaw is depressed by the contraction of the digastric, genio-hyoia, 

 mylo-hyoid and platysma myoides muscles; elevated by the temporal, 



