The completion of the book has been so slow that several chapters have been published successively in Mind, the Journal of Speculative Philosophy, the Popular Science Monthly, and Scribner's Magazine. Acknowledgment is made in the proper places. The bibliography, I regret to say, is quite unsystematic. I have habitually given my authority for special experimental facts; but beyond that I have aimed mainly to cite books that would probably be actually used by the ordinary American college-student in his collateral reading. The bibliography in W. Volkmann von Volkmar's Lehrbuch der Psychologie (1875) is so complete, up to its date, that there is no need of an inferior duplicate. And for more recent references, Sully's Outlines, Dewey's Psychology, and Baldwin's Handbook of Psychology may be advantageously used. Finally, where one owes to so many, it seems absurd to single out particular creditors; yet I cannot resist the temptation at the end of my first literary venture to record my gratitude for the inspiration I have got from the writings of J. S. Mill, Lotze, Renouvier, Hodgson, and Wundt, and from the intellectual companionship (to name only five names) of Chauncey Wright and Charles Peirce in old times, and more recently of Stanley Hall, James Putnam, and Josiah Royce. HARVARD UNIVERSITY, August 1890. CONTENTS. CHAPTER I. THE SCOPE OF PSYCHOLOGY, Mental Manifestations depend on Cerebral Conditions, 1. Pursuit of ends and choice are the marks of Mind's presence. CHAPTER II. THE FUNCTIONS OF THE BRAIN Reflex, semi-reflex, and voluntary acts. The Frog's nerve-centres. General notion of the hemispheres. Their Education--the Meynert scheme. The phrenological contrasted with the physiological conception. The localization of function in the hemispheres. The motor zone. Motor Aphasia. The sight-centre. Mental blindness. The hearing-centre. Sensory Aphasia. Centres for smell and taste. The touch-centre. Man's Consciousness limited to the hemispheres. The restitution of function. Final correction of the Meynert scheme. Conclusions. CHAPTER III. ON SOME GENERAL CONDITIONS OF BRAIN-ACTIVITY The summation of Stimuli. Reaction-time. Cerebral blood-supply, 97. Cerebral Thermometry. Phosphorus and Thought. CHAPTER IV. HABIT Due to plasticity of neural matter. Produces ease of action. Diminishes attention, 115. Concatenated performances. Ethical implications and pedagogic maxims. CHAPTER V. THE AUTOMATON-THEORY The theory described. Reasons for it. Reasons against it. CHAPTER VI. THE MIND-STUFF THEORY Evolutionary Psychology demands a Mind-dust. Some alleged proofs that it exists. Refutation of these proofs. Self-compounding of mental facts is inadmissible. Can states of mind be unconscious? Refutation of alleged proofs of unconscious thought. Difficulty of stating the connection between mind and brain. 'The Soul' is logically the least objectionable hypothesis. Conclusion. CHAPTER VII.