An English histologist remarked one day, with some eloquence, how little the most minute study of the brain aided us to understand thought. He was thus answering Auguste Comte, who, in a moment of aberration, claimed that psychology, in order to become a science, ought to reject the testimony of the consciousness, and to use exclusively as its means of study the histology of the nerve centres and the measurement of the cranium. Our histologist, who had passed part of his life examining, under the microscope, fragments of cerebral matter, in following the forms of the cells, the course of the fibres, and the grouping and distribution of the fascia, made the following remark: "It is the fact that the study, however patient, minute, and thorough it might be, of this nerve-skein can never enable us to know what a state of consciousness is, if we do not know it otherwise; for never across the field of the microscope is there seen to pass a memory, an emotion, or an act of volition." And, he added, "he who confines himself to peering into these material structures remains as ignorant of the phenomena of the mind as the London cabman who, for ever travelling through the streets of the great city, is ignorant of what is said and what is going on in the interior of the houses." This picturesque comparison, the truth of which has never been questioned, is based on this supposition, that the psychical act is entirely immaterial and invisible, and therefore escapes the piercing eye of the microscope. But a deeper analysis of the mind shows how little exact is this assertion. From the moment each psychical act implies a material object, we can ask ourselves two things: (1) Why is it that the anatomist does not discover these material objects in the interior of the brain? We ought to see them, for they are material, and therefore visible. We ought to see them with their aspect and colour, or be able to explain why they are not seen. In general, all that is described to us in the brain is the molecular vibrations. But we are not conscious of them. Where, then, is that of which we are conscious? (2) It should next be explained to us by what elaboration, transmutation, or metamorphosis a molecular disturbance, which is material, can transform itself into the objects which are equally material. This is the criticism we have to address to materialism. Until proof to the contrary, I hold it to be irrefutable. PARALLELISM