The lowest level, that of organic states, is typified by fatigue. The middle level, that of internal steer, is typified by the hunting dog, striving towards his prey, though not, as far as we know, having any clear idea of the result at which his actions are aimed. The highest level, that of conscious purpose, is represented by any one who knows exactly what he wants and means to get.
No single word in the language stands out clearly as the proper term to cover all three levels. "Motives" would serve, if we agree at the outset that a motive is not always clearly conscious or definite, but may be any inner state or force that drives the individual in a given direction. "Wants" or "needs" might be substituted for "motives", and would apply better than "motives" to the lowest of our three levels. "Tendencies", or "tendencies to reaction", carries about the right meaning, namely that the individual, because of his internal state, tends towards a certain action. "Determining tendencies" (perhaps better, "directive tendencies") is a term that has been much used in psychology, with the meaning that the inner tendency determines or directs behavior. Much used also are "adjustment" and "mental set", the idea here being to liken the individual to an adjustable machine which can be set for one or another sort of work. Often "preparation" or "readiness for action" is the best expression.
Organic States that Influence Behavior
Beginning at the lowest of our three levels, let us observe not even the simplest animal, but a single muscle. If we give a muscle electric shocks as stimuli, it responds to each shock by contracting. To a weak stimulus, the response is weak; [{73}] to a strong stimulus, strong. But now let us apply a long series of equal shocks of moderate intensity, one shock every two seconds. Then we shall get from the muscle what is called a "fatigue curve", the response growing weaker and weaker, in spite of the continued equality of the stimuli. How is such a thing possible? Evidently because the inner condition of the muscle has been altered by its long-continued activity. The muscle has become fatigued, and physiologists, examining into the nature of this fatigue, have found the muscle to be poisoned by "fatigue substances" produced by its own activity. Muscular contraction depends on the oxidation of fuel, and produces oxidized wastes, of which carbon dioxide is the best known; and these waste products, being produced in continued strong activity faster than the blood can carry them away, accumulate in the muscle and partially poison it. The "organic state" is here definitely chemical.
Fig. 22.--Fatigue curve of a muscle. The vertical lines record a series of successive contractions of the muscle, and the height of each line indicates the force of the contraction. Read from left to right.
This simple experiment is worth thinking over. Each muscular contraction is a response to an electric stimulus, but the force of the contraction is determined in part by the internal state of the muscle. Fatigue is an inner state of the muscle that persists for a time (till the blood carries away the wastes), and that predisposes the muscle towards a certain kind of response, namely, weak response. Thus the three characteristics of purposive behavior that seemed so [{74}] difficult to fit into the scheme of stimulus and response are all here in a rudimentary form.
But notice this fact also: the inner condition of muscular fatigue is itself a response to external stimuli. It is part and parcel of the total muscular response to a stimulus. The total response includes an internal change of condition, which, persisting for a time, is a factor in determining how the muscle shall respond to later stimuli. These facts afford, in a simple form, the solution of our problem.
Before leaving the muscle, let us take note of one further fact. If you examine the "fatigue curve" closely, you will see that a perfectly fresh muscle gains in strength from its first few responses. It is said to "warm up" through exercise; and the inner nature of this warming up has been found to consist in a moderate accumulation of the same products which, in greater accumulation, produce fatigue. The warmed-up condition is then another instance of an "organic state".