GENERAL VIEW OF THE HUMAN SYSTEM. 15 



NUTRITION. 



All these parts are in incessant action, which exhausts the fluids, 

 and wastes the solids ; to obviate this, the frame is endued with 

 the powers of nutrition. The teeth prepare our food for this pur- 

 pose ; those in front, sharp and thin, to receive and cut the food ; 

 those behind, broad and strong, indented like the surface of a mill- 

 stone, with small cavities, the better to fit them for grinding it. As 

 milk is our food for some time after we are born, and as teeth would 

 hurt the tender nipple, nature has wisely postponed the appearance 

 of teeth until they become necessary. All our other bones are 

 covered with a very fine skin, but this covering is omitted on the 

 teeth, as chewing would then have been attended with exquisite 

 pain. Had they been uncovered, they would have been subject to 

 injuries from the air, and to the penetration of liquors that would 

 destroy them, to guard against which they are curiously covered 

 with a fine white enamel, harder than the bone itself. 



Growing as they do in rows, numerous, and none rising higher 

 than the other, they form a regular and beautiful addition to the 

 mouth. To their aid, they also call in the tongue and lips, the 

 latter keep the food in the mouth, while the tongue returns it to 

 the renewed attrition of the grinders ; the motion of the cheeks at 

 the same time, with the stimulus of food in the mouth, presses out 

 from a variety of reservoirs a moistening liquor necessary to pre- 

 pare the food for digestion, as well as to soften and facilitate its 

 passage into the stomach when the mouth is inactive, these 

 fountains are mostly at rest, but when we eat or speak their 

 assistance is always ready. 



As the food passes the wind-pipe, before it enters the cesophagus 

 or gullet, there is a valve provided, which shuts on the approach 

 of any substance, but the moment it has passed, it opens again ; we 

 all know what uneasiness is created by the smallest morsel going 

 the wrong way ; which if not thus guarded would expose us to 

 instant death, by admitting any substance on the lungs. 



The muscles of the gullet are contrived to pass our food quickly, 

 but the stomach is constituted to retain its contents, which are 

 lodged in the centre and made soft by the most kindly combination 

 of heat and humidity. From whence, after being reduced to the 

 most nicely mixed pulp, they are dislodged by a gently acting 

 force and pass into the intestines ; where, meeting the bile and 

 pancreatic juices, it is passed by the vermicular, or peristaltic 



