The fatigue which we observe in the arms and legs has accordingly its real seat in the brain; just as the pain which these parts feel is really experienced in the brain; for it is connected with the motor nerves, as with the nerves of sense. The muscles which are not actuated from the brain – for example, those of the heart – accordingly never tire. The same grounds explain the fact that both during and after great muscular exertion we cannot think acutely. That one has far less energy of mind in summer than in winter is partly explicable from the fact that in summer one sleeps less; for the deeper one has slept, the more completely awake, the more lively, is one afterwards. This, however, must not mislead us into extending sleep unduly, for then it loses in intension, i.e., in deepness and soundness, what it gains in extension; whereby it becomes mere loss of time. This is what Goethe means when he says (in the second part of "Faust") of morning slumber: "Sleep is husk: throw it off." Thus in general the phenomenon of sleep most specially confirms the assertion that consciousness, apprehension, knowing, thinking, is nothing original in us, but a conditioned and secondary state. It is a luxury of nature, and indeed its highest, which it can therefore the less afford to pursue without interruption the higher the pitch to which it has been brought. It is the product, the efflorescence of the cerebral nerve-system, which is itself nourished like a parasite by the rest of the organism. This also agrees with what is shown in our third book, that knowing is so much the purer and more perfect the more it has freed and severed itself from the will, whereby the purely objective, the æsthetic comprehension appears. Just as an extract is so much the purer the more it has been separated from that out of which it is extracted and been cleared of all sediment. The opposite is shown by the will, whose most immediate manifestation is the whole organic life, and primarily the untiring heart.
This last consideration is related to the theme of the
