First edition of Durand’s early work of behavioral psychology. His essays on the physiology of perception and the relationship of the mind to the outside world do not, by his own admission, use groundbreaking medical observations, but he readdresses well-versed scientific knowledge with philosophical questions, such as the morality of reflexive actions. The final essay contains a semi-critical response to positivism and Comte’s ‘general science of things’, with Durand proposing his own methodological structure or taxonomy of ideas.