It is the custom of our times to explain neurological, and, to some extent, psychiatric disorders by reference to a static or diagrammatic conception of the physiology of the nervous system, linked with the findings of morbid anatomy. But, in the words of Riese (1950), expressed in his Principles of Neurology:

“Can the behaviour of a living organism be interpreted as purely mechanical? Though the organism remains submitted to the law of mechanics and physics, and though it is to the benefit of a steady improvement of our factual knowledge to explore the mechanics to the maximum possible, we must recognize that in a living organism mechanics are not left to themselves (which means to chance), but that they are at the service of a directing agency best described as the organism's welfare. The reflex must be conceived as an instrument of this agent. All disorders analysed and described in terms of reflex action are only instrumental ones. Neither the physician's task nor his possibilities extend beyond this limit. The directing forces of the organism will be withheld forever from the physician's acting power, if only for the reason that these forces are just ideas or principles of interpretation, but not perceptible realities.”