THE DIGESTIVE FUNCTION, ETC. 



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Oavity of some kind or other in which the food is digested ; an agreement 

 which ma)! be regarded as one of the leading features by which the animal 

 structure is distinguished from the vegetable. 



Let us then, in the first place, trace this cavity as it exists in man, and 

 the more perfect animals ; the organs which are supposed to be auxiliary 

 to it, and the powers by which it accompHshes its important trust. Let v 

 us next observe the more curious deviations and substitutes that occur in 

 classes that are differently formed : and lastly, let us attend to a few of the 

 more singular anomalies that are occasionally met with, and especially in 

 animals that are capable of subsisting on air or water alone, or of enduring 

 very long abstinences or privations of food. 



The alimentary cavity in man extends from the mouth through the 

 whole range of the intestinal canal :* and hence its different parts are of 

 very different diameters. In the mouth, where it commences, it is wider ; 

 it contracts in the esophagus or gullet ; then again widens to form the sto- ,i 

 mach, and afterwards again contracts into the tube of the intestines. This 

 tube itself is also of different diameters in different parts of its extent ; and v 

 it is chiefly on its diversity of magnitude, that anatomists have established 

 its divisions. Its general length is five or six times that of the man him- 

 self ; and in children not less than ten or twelve times, in consequence of 

 their diminutive stature. In some animals it is imperforate ; it is so occa- 

 sionally in birds, and fishes, and almost uniformly so in zoophytes. 



Generally speaking, the extent of the digestive cavity bears a relation to 

 the nature of the aliments by which the Individual is designed to be nour- 

 ished. The less analogous these aliments are to the substance of the ani- 

 mal they are to sustain, the longer they must remain in the body to under- 

 go the changes that are necessary to assimilate them. Hence the intesti- 

 nal tube of herbivorous animals is very long, and their stomach is extremely 

 large, and often double or triple ; while the carnivorous have a short and 

 straight digestive canal, the food on which they feed being already of their 

 own nature, and containing^ a larger quantity of nourishment in a less bulk ; 

 and hence demanding a smaller proportion both of time and space to be- 

 come fit for use. In this respect man holds a medium between the two : 

 his digestive canal is less complex than that of most animals that feed on 

 , grass alone, and more extensive than that of most animals that are confined 

 j to a diet of their own kind. Man is hence omnivorous, and is capable of 

 subsisting on an aliment of either sort : and from his digestive organs, as 

 well as from various others, is better qualified for every variety of soil and 

 I chmate than any other animal. 



j Man, however, is by no means the only omnivorous animal in the world : 

 for the great Author of nature is perpetually showing us that though he ope- 

 rates by general laws, he is in every instance the lord and not the slave of 

 them. Hence, among quadrupeds, the swine, and among insects, the ant, 

 possesses as omnivorous a power as man himself, and feeds equally on the 

 fleshy parts of animals, and on grain, and the sweet juices of vegetables. In 

 consequence of this omnivorous power in the ant, we may often make 

 use of him as a skilful anatomist ; for, by putting a dead frog, mouse, or 

 other small animal in a box perforated with holes, and placing it near an 

 ant-hill, we shall find it in a few days reduced to a perfect and exquisite 

 skeleton, every atom of the soft parts being separated and devoured. 

 The mild materials of the food are first masticated and moistened in the 



* Stud, of Med. ii, 2. 



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