re" by a man and
the incubatory instinct of a bird is inexact. The man avoids fire when
he has had experience of the pain produced by burning; but the bird
incubates the first time it lays eggs, and therefore before it has had
any experience of incubation. For the comparison to be admissible, it
would be necessary that a man should avoid fire the first time he saw
it, which is notoriously not the case.

The term "instinct" is very vague and ill-defined. It is commonly
employed to denote any action, or even feeling, which is not dictated by
conscious reasoning, whether it is, or is not, the result of previous
experience. It is "instinct" which leads a chicken just hatched to pick
up a grain of corn; parental love is said to be "instinctive"; the
drowning man who catches at a straw does it "instinctively"; and the
hand that accidentally touches something hot is drawn back by
"instinct." Thus "instinct" is made to cover everything from a simple
reflex movement, in which the organ of consciousness need not be at all
implicated, up to a complex combination of acts directed towards a
definite end and accompanied by intense consciousness.

But this loose employment of the term "instinct" really accords with the
nature of the thing; for it is wholly impossible to draw any line of
demarcation between reflex actions and instincts. If a frog, on the
flank of which a little drop of acid has been placed, rubs it off with
the foot of the same side; and, if that foot be held, performs the same
operation, at the cost of much effort, with the other foot, it certainly
displays a curious instinct. But it is no less true that the whole
operation is a reflex operation of the spinal cord, which can be
performed quite as well when the brain is destroyed; and between which
and simple reflex actions there is a complete series of gradations. In
like manner, when an infant takes the breast, it is impossible to say
whether the action should be rather termed instinctive or reflex.

What are usually called the instincts of animals are, however, acts of
such a nature that, if they were performed by men, they would involve
the generation of a series of ideas and of inferences from them; and it
is a curious, and apparently an insoluble, problem whether they are, or
are not, accompanied by cerebral changes of the same nature as those
which give rise to ideas and inferences in ourselves. When a chicken
picks up a grain, for example, are there, firstly,