188 ALIMENTATION. 



teenth day, with all the appearances of inanition. Another fed on barley 

 alone died in the same way during the fourth week. The third was fed 

 alternately day by day with potato and barley, for three weeks, and afterward 

 with potato and barley given together. This animal increased in size and 

 was perfectly well nourished. 



In 1769, long before any of the above-mentioned experiments were per- 

 formed, Dr. Stark, a young English physiologist, fell a victim at an early age 

 to experiments on his own person on the physiological effects of different 

 kinds of food. He lived for forty-four days on bread and water, for twenty- 

 nine days on bread, sugar and water, and for twenty-four days on bread, 

 water and olive-oil ; until finally his constitution became broken, and he died 

 from the effects of his experiments. 



CHAPTEE VII. 



DIGESTION MASTICATION, INSALIVATION AND DEGLUTITION. 



Prehension of food Mastication Physiological anatomy of the teeth Anatomy of the maxillary bones 

 Temporo-maxillary articulation Muscles of mastication Action of the tongue, lips and cheeks in 

 mastication Parotid saliva Submaxillary saliva Sublingual saliva Fluids from the smaller glands of 

 the mouth, tongue and fauces Mixed saliva Quantity of saliva General properties and composition 

 of the saliva Action of the saliva on starch Uses of the saliva Physiological anatomy of the parts 

 concerned in deglutition Mechanism of deglutition First period of deglutition Second period of deg- 

 lutition Protection of the posterior nares during the second period of deglutition Protection of the 

 opening of the larynx and uses of the epiglottis in deglutition Third period of deglutition Deglutition 

 of air. 



alimentary substances are, with few exceptions, introduced 

 in the form in which they exist in the blood and require no preparation or 

 change before they are absorbed; but organic nitrogenized substances are 

 always united with more or less matter possessing no nutritive properties, 

 from which they must be separated, and even when pure, they always undergo 

 certain changes before they are taken up by the blood. The non-nitrogenized 

 matters also undergo changes in constitution or in form preparatory to ab- 

 sorption. 



'Prehension of Food. Prehension of food in the adult is a process so 

 simple and well known that it demands little more than a passing mention. 

 The mechanism of sucking in the infant and of drinking is a little more 

 complicated. In sucking, the lips are closed around the nipple, the velum 

 pendulum palati is applied to the back of the tongue so as to close the buccal 

 cavity posteriorly, and the tongue, acting as a piston, produces a virtual 

 vacuum in the mouth, by which the liquids are drawn in with considerable 

 force. This may be done independently of the act of respiration, which is 

 necessarily arrested only during deglutition ; for the mere act of suction has 

 never anything to do with the condition of the thoracic walls. The mechan- 

 ism of drinking from a vessel is essentially the same. The vessel is inclined 



