This mental activity, at first involuntary under the pressure of illness and suffering, gradually became second nature and led me finally to recognize that I was but an automaton devoid of free will in thought and action and merely responsible to the forces of the environment. Our bodies are of such complexity of structure, the motions we perform are so numerous and involved and the external impressions on our sense organs to such a degree delicate and elusive, that it is hard for the average person to grasp this fact. Yet nothing is more convincing to the trained investigator than the mechanistic theory of life which had been, in a measure, understood and propounded by Descartes three hundred years ago.

My Inventions (1919)