Doctor Who_ The Banquo Legacy - Andy Lane [13]
He had two of them in a wooden cage on one of the packed windowsills, jammed between a collection of wires and metal pins and a pile of notes. I had not noticed it earlier, but as Harries picked his way over to the window I saw the brown blur of movement from within. He brought the cage to the table, seeming not to notice the papers following in its wake. Before he opened the cage he again turned his attention to the maze, flicking hinged sections of the long walls across the corridors inside until the geography of the course from the centre to the opening at the side near the cage was completely altered. Then he opened the lid of the cage and reached inside.
The two rats looked identical in size, colour and markings. As I watched Harries lift out the nearer of the two, I wondered why people felt so nervous and revolted by the small creatures, which seemed after all only large mice. Its companion watched silently from the cage, its small eyes glinting between the slats. But as Harries placed the first rat in the open area of the square heart of the maze, a long segmented tail unwound into my view as if with a venomous life of its own. And when the rat paced the inside of its prison, exploring the several passages leading off, it was as if the tail was a separate animal pushing the furry body ahead of itself as it coiled and snaked in the rat’s shadow. I swallowed dryly, and wondered no longer.
Harries seemed unaffected by the animal, and watched closely as it scuttled into corners and retraced its steps, becoming more and more frantic as it found its way blocked. He spoke the whole time, his voice racing like the rat’s feet, his eyes darting like its tail. I did not hear all of what he said for the rat held me fascinated with its movements, and what I understood of what I heard seemed unconnected with what I saw.
‘A hundred years ago Galvani stimulated living tissue with electric current. We now know that a potential difference exists between the cut ends of muscle fibre and the intact external surface bathed in saline solution… Nernst explains this as the positive and negative ions in the solution moving towards equilibrium. Somewhat simplistic perhaps, but he is right.’
The rat scratched at a hinge for a moment, than gave up and retraced its steps, discovering a new turning and darting into it, tail lingering for a moment cautiously before following.
‘I submit that this biopotential in living tissue is due to variations in the potassium ion concentration of the cell membrane. Thus nervous impulses, and even the workings of the brain itself, are electrical in nature… I have found that there are four types of brainwave, distinguished by their pulse frequency…’
I lost him for a while as he explained, more to himself than to me, about how each brainwave signified or indicated a different level of brain activity, from deep sleep to anxiety or great mental disturbance.
‘You are satisfied that this rat is unable to escape my maze?’ Harries said, and it took me a moment to realise that he was not still talking about brains, and inducing a ‘smoothly fluctuating magnetic field about the cerebellum by means of a driving current applied to electrodes on the skull’, to which he had moved on. Before I could reply, he had removed the rat from the maze and replaced it in the cage, pulling out its fellow as he did so. ‘Let us see how your brother fares,’ he murmured and set the second rat down in the central space. As it too struggled to escape, Harries continued from where he had left off:
‘The field is started at a frequency of ten cycles per second, then reduced slowly to one. When the change in modulated brain waves from the cerebellum is detected, the amplitude of the driving waves is increased to cause resonance inside the brain cavity. Positive wave reinforcement causes the output to rise sharply to an easily detectable level.’
He paused, eyes still following the