In every department of animal life, also, the principle appears to exist, and exhibits itself in the conduct of all free agents, from the insect to the elephant. The dog that has been kindly treated in a particular house, seldom fails to visit it again; and when he is violently driven from another, the same principle indisposes him to return. It is upon record, that a surgeon who had bandaged the broken leg of a dog, was afterwards visited by his patient, who brought another, requiring a similar operation. The horse, in like manner, is proverbially sagacious in the application of his knowledge. Mismanagement in a groom in one instance, may create a "vice," which may lessen his value during life. This "vice," which is confirmed by practice, is nothing more than the repeated application of his knowledge. Such a "vice," accordingly, is best cured by avoiding the circumstances which originally gave rise to it, till it dies from his memory. Many other instances of a similar kind in the lower animals will readily occur to the reader, all of which lead directly to the conclusion, that, even in the brute creation, Nature not only prompts them to collect information from what happens around them, and to act in correspondence to its indications; but that, in fact, all the knowledge they receive, or are capable of acquiring above instinct, is retained or lost, exactly in proportion as it is, or is not, put to use. In the case of rational creatures, this great design of Nature is still more distinctly marked,--is intended for more important purposes,--and is carried on by a separate system of internal machinery, part of which at least is peculiar to man. This system of mental machinery consists of two kinds, one of which may, we think, with propriety get the popular name of the "Animal, or Common Sense," and the other has already received the appropriate name of "The Moral Sense," or conscience. To Nature's method of using these principles, for prompting and directing us in the use of our knowledge, we shall now shortly advert. CHAP. IX. _On Nature's Methods of Applying Knowledge by the Principle of the Animal, or Common Sense._ When an infant, by laying hold of a hot tea-pot burns its hand, it refuses to touch it again;--when a child has been frightened from a park or field, he will not willingly enter it a second time;--and when any thing is thrown in the direction of the head, we instantly stoop, or bend to one side, to evade it. These are instances of the application of knowledge, by the principle of "common sense," which do not belong to instinct; and, in many cases at least, anticipate the exercise of reason. Our object at present, however, is with the principle, and not with its name.