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 exactly analogous character. He makes no assumptions as to their special nature; in particular, he rejects as hypothetical, or at least as needless for his purpose, the picture-mechanism of cells and fibres upon which the associationists rely. His only postulates are that the brain, as a living thing, requires both nourishment and exercise, and that in response to the stimuli of a hostile environment it strives to maintain a ‘vital maximum’. Practically, however, he makes the further general assumption that it is capable by internal organisation and outward action of progressively increasing its possible maximum. The ideal maximum would be reached in complete adaptation to an all-comprehensive environment. Physiological processes therefore correspond in type to the mental series. A vital disturbance is either cancelled by other internal changes or removed by a motor response. The stimulus, however, which starts the series need not be, and usually is not, merely injurious. Work is as necessary as nourishment, activity as indispensable as rest. Through response to stimuli the brain organises more and more complex vital series which by enabling it to maintain itself with greater ease in the given environment release energy for more extended activities. In determining, by general dialectical argument, the various types to which such vital series must conform, Avenarius professes to have sketched the programme of future physiological research.

From this point of view Avenarius states the parallelism of psychical and physical in quite a fresh light. He frees the doctrine from dependence upon any particular set of views as to the constitution and working of the nervous system, and yet brings the two series more closely together than had ever been done on any previous theory. Indeed, just on that account he maintains that his view is not properly describable as parallelism. For, while parallelism implies dualism, the relation which he himself traces between the mental and the physiological series is of the same nature as that which exists between the factors in a mathematical function. There is a point for point correspondence which is, he claims, absolutely complete. In this logical functional relation there is no more dualism than exists between the premisses of an argument and the conclusion in which they result.

One very important feature of his position remains for consideration—a feature which is very puzzling to any