Lecture XVI

I will now draw your attention to something you can very well observe if only you are prepared to extend your observation to wider fields. Namely, however easily man may emancipate himself from the Universe in the alternation of sleeping and waking as regards time, he cannot with impunity emancipate himself as regards spatial position. Sophisticated folk—for such there are—may turn night into day, day into night, but even they, when they do go to sleep, must adopt a position other than the upright one of waking life. They must, as it were, bring the line of their spine into the same direction as the animal's. One might investigate a thing like this in greater detail. For instance, it is a physiological fact that there are people who in conditions of illness cannot sleep properly when horizontal but have to sit more upright. Precisely these deviations from the normal association of sleep with the horizontal posture will help to indicate the underlying law. A careful study of these exceptions—due as they are to more or less palpable diseases (as in the case of asthmatic subjects for example)—will be indicative of the true laws in the domain. Taking the facts together, you can quite truly put it in this way: To go to sleep, man must adopt a position whereby his life is enabled in some respects to take a similar course, while he is sleeping, to that of animal life. You will find further confirmation in a careful study of those animals whose spinal axis is not exactly parallel to the Earth's surface.