Granted, however, that a felt need of some kind, indefinite at first but none the less real, is present in many cases as a spur to instinctive behaviour; is it in all cases a necessary factor? May we say that this distinguishes instinctive from merely reflex action? The question is, from the nature of the case, exceedingly difficult to answer. But without going so far as to say that reflex action may be unerringly distinguished from instinctive behaviour by the absence of any such internal factors, we may perhaps, at any rate, go so far as to give provisional acceptance to the view that in instinct these wants and felt needs enter into the conscious situation in a manner and to a degree that are so far distinctive--which seems to be the position adopted by Professor Wundt. There is, however, a further relation between the external stimulus and these internal factors which is presumably of no little importance. The stimulus intensifies the want, or may in some cases call it into existence. Just as a whiff from the kitchen may lead us to realize that we need the satisfaction that will erelong be presented at table, so may the sight of his mate in the spring evoke in the breast of the yearling sparrow a need, having its source in morphological and physiological changes, that spurs him on to the courtship that shall lead to its due satisfaction. Popular attention has, indeed, been so naturally drawn to the internal needs or wants with which we are now dealing, as to give them an almost exclusive monopoly of the term “instinct,” which thus often comes to be regarded as a connecting link between the stimulus and the act. The sight of a mouse, for example, is said to call forth the instinct of the cat, which is satisfied by her pouncing upon it. And so it comes about that, while the biologist fixes upon the instinctive act as the essential feature, the psychologist is apt to regard the impulse[41] which prompts to action as the more central and characteristic element. We are here endeavouring to combine both these points of view.