Merely because something has gone wrong in some blood-vessel or nerve-fibre, all my strength and intelligence seem to fail me.

The same might happen in the case of a bone, of a cartilage, or of a nerve-fibre.

Here it is evident that there can be no rods and cones, their place being wholly occupied by strands of nerve-fibre.

So, in the brain, every sensation is the ring of a cerebral particle, the effect of a momentary impulse sent along a nerve-fibre.