In considering the Physical Basis a large place must be assigned to the mechanical and chemical relations which are involved in organic functions; yet we have to recognize that this procedure of Analysis is artificial and preparatory, that none of its results are final, none represent the synthetic reality of _vital_ facts. Hence one leading object of the following pages has been everywhere to substitute the biological point of view for the metaphysical and mechanical points of view which too often obstruct research--the one finding its expression in spiritualist theories, the other in materialist theories; both disregarding the plain principle that the first requisite in a theory of biological phenomena must be to view them in the light of biological conditions: in other words, to fix our gaze upon what passes in the organism, and not on what may pass in the laboratory, where the conditions are different. Analysis is a potent instrument, but is too often relied on in forgetfulness of what constitutes its real aid, and thus leads to a disregard of all those conditions which it has artificially set aside. We see this in the tendency of anatomists and physiologists to assign to _one_ element, in a complex cluster of co-operants, the significance which properly belongs to that cluster: as when the property of a tissue is placed exclusively in a single element of that tissue, the function of an organ assigned to its chief tissue, and a function of the organism to a single organ. Another object has been to furnish the reader uninstructed in physiology with such a general outline of the structure and functions of the organism, and such details respecting the sentient mechanism, as may awaken an interest in the study, and enable him to understand the application of Physiology to Psychology. If he comes upon details which can only interest specially educated students, or perhaps only by them be really understood, he can pass over these details, for their omission will not seriously affect the bearing of the general principles. I have given the best I had to give; and must leave each reader to find in it whatever may interest him. The uses of books are first to stimulate inquiry by awakening an interest; secondly, to clarify and classify the knowledge already gained from direct contemplation of the phenomena. They are stimuli and aids to observation and thought. They should never be allowed to see for us, nor to think for us.