I. All those internal motions of animal bodies, which contribute to digest their aliment, produce their secretions, repair their injuries, or increase their growth, are performed without our attention or consciousness. They exist as well in our sleep, as in our waking hours, as well in the foetus during the time of gestation, as in the infant after nativity, and proceed with equal regularity in the vegetable as in the animal system. These motions have been shewn in a former part of this work to depend on the irritations of peculiar fluids, and as they have never been classed amongst the instinctive actions of animals, are precluded from our present disquisition.
But all those actions of men or animals, that are attended with consciousness, and seem neither to have been directed by their appetites, taught by their experience, nor deduced from observation or tradition, have been referred to the power of instinct. And this power has been explained to be a _divine something_, a kind of inspiration; whilst the poor animal, that possesses it, has been thought little better than _a machine_!
The _irksomeness_, that attends a continued attitude of the body, or the _pains_, that we receive from heat, cold, hunger, or other injurious circumstances, excite us to _general locomotion_: and our senses are so formed and constituted by the hand of nature, that certain objects present us with pleasure, others with pain, and we are induced to approach and embrace these, to avoid and abhor those, as such sensations direct us.
Thus the palates of some animals are gratefully affected by the mastication of fruits, others of grains, and others of flesh; and they are thence instigated to attain, and to consume those materials; and are furnished with powers of muscular motion, and of digestion proper for such purposes.
These _sensations_ and _desires_ constitute a part of our system, as our _muscles_ and _bones_ constitute another part: and hence they may alike be termed _natural_ or _connate_; but neither of them can properly be termed _instinctive_: as the word instinct in its usual acceptation refers only to the _actions_ of animals, as above explained: the origin of these _actions_ is the subject of our present enquiry.