ABSTRACT
Modern physiology begins with Descarte's theory that animals are machines, while men are machines with the addition of a soul, which he located in the pineal gland in the middle of the brain. The theory that animals were machines therefore became possible, and as soon as it became possible to propound it without risking one's life, Descartes did so. In the case of man only, the soul was superadded. The eighteenth-century materialists discarded the human soul; and if modern brain surgery has not completely disproved its existence, it has at least shown that it is possible to remove the pineal gland without destroying consciousness and will. On the contrary it is possible, without denying the validity of physical laws, to adapt biological theory to biological practice by saying that the organism is something more than a machine, in the sense that it has a unity of a type which the machine lacks.
