116 ON ZOOLOGY. 



those wonderful effects are produced, that confer 

 so much dignity and interest upon the subject. 



One of the first propensities of animals, and 

 which, as being essential to their very existence, 

 may be considered the most important, is the 

 gratification of hunger ; through the agency of 

 which, the vital principle is preserved, and the 

 several parts of the animal system kept in due 

 tone. To promote this sensation, nature has 

 caused the stomach of animals to secrete a very 

 active fluid, denominated the gastric juice, which, 

 possessing a solvent power over various sub- 

 stances, contributes in a very remarkable degree 

 to their digestion. As soon therefore as the lat- 

 ter process has been completed and the stomach 

 becomes empty, the gastric fluid acts directly 

 upon its internal coats, and causing their fibres to 

 contract, it produces that pain or disagreeable 

 sensation which we denominate hunger; and as 

 this is only to be relieved by a fresh application 

 of extraneous matter, animals are instinctively 

 taught to seek out those substances, which, under 

 the denomination of food, are the best calculated 

 to relieve the uneasiness ; nature having bestowed 

 on them the faculty of taste, to enable them to 

 discriminate and avoid injurious articles, and to 

 relish their food, so that it be taken in due pro- 

 portions, and be sufficiently divided, previously 

 to its undergoing those future processes upon 

 which its ultimate digestion is made to depend. 



