INTRODUCTION
11
and that progress has taken place by the slow acquirement of more specific reactions. This has occurred not only in consequence of the development of sense organs of higher capacity, but, to an even greater extent, by increasingly perfect integration of afferent impulses at various sensory levels. Finally, in man sensation is a highly differentiated reaction to physiological processes which have undergone profound transformations on their way from the peripheral end-organs to the highest receptive centres.
