There is another class of actions, which are of a pecu liar nature, and are generally classed together as depend ing upon the same principle, which are styled instinctive. Instinct may be defined a capacity for performing actions which are voluntary, and immediately conduce to some useful purpose, but which are not acquired by experience, and of the object of which the animal is entirely ignorant. The case of the bird building its nest has been frequently referred to as an example of an instinctive action. The animal, although it may have been taken from its mother immediately after it left the shell, and been since kept con fined in a cage, previously to laying its eggs, will prepare its nest with as much skill as if it had lived among other birds, and built a nest for a number of successive seasons; yet it cannot be directed either by imitation or by reason, nor can we suppose that there is any direct impression made upon any part of the body which can bring about the effect. It would seem that in this case a particular state of the brain exists, which leads to a certain action, similar to what in other cases is induced by imitation, as sociation, or by reason. There are other kinds of instinct, where we can trace the effect produced to a direct impres sion upon a nerve or organ of sense, such as where the smell prevents an animal from eating food which is not adapted to the state of its digestive organs. Here the impression upon the olfactory nerve is alone sufficient to produce an effect, which in the human species is derived from a more complicated feeling, partly from instruction, partly from association, and in part from reason, combined probably, in some degree, with an immediate effect upon the organs of sense.
The phenomena of instinct appear to be so clearly marked among the inferior animals, that its existence, as applicable to them, has been seldom doubted, and except Darwin, there is perhaps no writer who has attempted to argue directly against it. He proceeds upon the princi ple, that as instinct is a kind of blind impulse, directly the reverse of reason, it should always proceed in the same uniform track, and he endeavours to show that in those ac tions, which are generally regarded as instinctive, such as the building of nests, we discover some symptoms of rea son, in the adaptation of means to peculiar and extraordi nary circumstances. But to this argument it may be re plied, that in contending for the operation of instinct we do not propose entirely to exclude that of reason ; on the contrary, it is more probable that they both co-operate to the same end, the one supplying the deficiences of the other. But there is no ground for concluding that instinct consists in this blind direction to certain objects, it seems rather to prompt the animal to perform the action in the manner the best adapted for the object in view, so far re semhling the effect of reason, but differing from reason in the mode in which the impression is received into the mind.
It has been a subject of discussion among metaphysicians, whether man possesses the faculty of instinct, or whether the actions, which at first view resemble instinct, may not with more propriety be referred to other principles. The disciples of Locke are, for the most part, disposed to deny the existence of instinctive actions, and refer to asso ciation, habit, sympathy, or to some other principle, the effects which other writers have referred to instinct. Reid,
on the contrary, and his followers, suppose that many of our operations are innate or instinctive, depending upon the nature or original laws of our constitution, indepen dent of any circumstances, either internal or external. That the latter class of philosophers have unnecessarily multi plied these innate actions, and even, on some occasions, carried them to a ridiculous excess, is generally admitted, but, on the other hand, we conceive that their antagonists have not unfrequently failed in their attempts to explain various operations of the animal economy by their favou rite doctrine of association. We are disposed to conclude, with respect to this point, that while brutes are guided principally by instinct, combined with some portion of reason, man, although possessed of an infinitely higher de gree of reason, is not without some share of instinct.
Although the imagination is a faculty of a purely intel lectual nature, yet its action upon the body and its func tions is so remarkable, as to render it necessary for us to notice it in this place. It acts not only upon the nervous system, which might be supposed more adapted for its operations, but likewise upon the circulation, the respira tion, and the digestion ; in short, it is one of the most powerful agents over the animal economy. The history of medicine abounds with examples of the effect of the imagination, so that it frequently requires the greatest sa gacity in the practitioner, to distinguish between the phy sical effects of remedies and their effect upon the imagi nation. Some of the most remarkable illustrations of the power of the imagination were afforded by the operations of animal magnetism, and more lately by those of the me tallic tractors. Indeed, so powerful was the influence of the tractors over the body, and so much beyond any thing that could have been anticipated, that it was a long time before the imposition was detected, not indeed until it had been proved that, by proper management, similar effects might be produced without the aid of these supposed agents. In this point of view, the experiments of Dr. Haygarth are of great value, where he imitated the ope ration of the tractors, in the removal of severe and obsti nate diseases, by applying bits of wood to the patients, while their minds were impressed with the belief that they were to receive some mysterious influence from the appli cation. He found, that in this way obstinate pains of the limbs, that had long resisted all remedies, were suddenly removed, joints that were immovable were restored to motion, and, in short, it became difficult to say how far its operations might not extend. We can have no doubt, that in this way we are to account for some of the pretended mi racles of the ignorant and dark ages ; many of the wonder ful tales that are on record are actually true, but the infer ence that was drawn from them is false, and we must as crihe to the imagination of the patients themselves, the effects which they attributed to supernatural agency.