"Considering them however in their origin, they together represent a certain form of the transmission of force.... Some kinds of impressed force are followed by movements of retraction and withdrawal, others by such as secure a continuance of the impression. These two kinds of contraction are the phenomena and external marks of pain and pleasure respectively. Hence the tissue acts so as to secure pleasure and avoid pain by a law as truly physical and natural as that whereby a needle turns to the pole, or a tree to the light.... Hence, the law of Self-Conservation, or of the direction of Action, is merely another mode of expressing the fundamental property of animal tissue, which we have every reason to believe is derived from the more elementary physical properties of matter. The course of action is just as dependent on physical laws as that of a stone which falls to the ground. The belief in external consciousness makes no difference either way; the earliest phenomena of such consciousness are those of pleasure and pain, therefore we can suppose it to exist only as pleasure and pain. In the one case we say that action aims at, or naturally results in, the phenomena of pleasure; in the other case that it aims at the actual consciousness of pleasure. "The expression of impressed force, or the connection of action and sensation, is at first in the unorganized tissue direct and immediate, without the agency of nervous communication, or to return again to the ordinary psychological language, is unintentional or involuntary.... The earliest modification is due to association, whereby secondary sensations, or (as they are called later when they become perceived) ideas are produced. These manifest themselves as weaker repetitions of the primary pleasures and pains, and, therefore, are naturally followed by like results.... The process is this: the force originally impressed by the first sensation, instead of being all expressed in action, is partly induced by habituation into an internal channel, and so transformed into the kind of force which generally impresses the second kind of sensation, and this now produces its appropriate action. Hence part of the original force has undergone two transformations instead of one; the immediate antecedent of action being the force produced by association, or in other words, the associated pleasure. This is the rudiment of _motive_, which, however, is not generally called by that name till it is _perceived_. The same process may go on through two or more links of association; the first transformed force being again transformed internally instead of expressed, and the second again in its turn, until eventually a transformation is reached which finds its easiest way of escape in action; the immediate motive power being that transformation of force, or that associated pleasure, which immediately precedes the action. Actions of this kind constitute the lower phenomena