Up to a comparatively recent date, our conception of the nervous system was that it was built up of nerve cells and nerve fibres, more or less intimately bound together by a peculiar kind of tissue known as neuroglia. It was further supposed that, in the central nervous organs, nerve cells were linked together by processes passing from one cell to another, that sensory nerve fibres passed into, and were in their substance continuous with, nerve cells, and that motor fibres originated in nerve cells, and passed out to muscle fibres. It was also held that the elements of sensory organs, such as the retina or the organ of Corti, were organically connected with nerve cells in the cerebral organs. In short, the nervous system, as a whole, was held to be composed of cells and fibres closely connected together, so that the structure was like a vast web, the size of the meshes of which would vary according to the intricacy of the connections by which the various cellular elements were held together by nerve fibres. These histological conceptions were founded on the microscopical scrutiny of sections prepared by the older methods of hardening and staining, from the time of Lockhart Clarke to nearly the present day.

The notions of physiologists, as is usually the case, were more or less in conformity with, and were influenced by, these histological conceptions. Nerve cells were supposed to be excited by nervous impulses, or to originate nervous impulses, and nervous impulses appeared to pass from cell to cell.