The law of the conservation of energy is purely a reading of the physical facts, _i.e._ of the play of world-events in so far as it manifests itself in the form of reversible processes--thus, as re-actual; and as such is also recognized by physicists of intelligence.[37] At this point, however, the biologist enters and plays the part of the countryman at the theatre by taking the picture for the reality itself. He argues with that logical acuteness such as is only possible where no actuality stands in its way: “If the law of the conservation of energy is really a universal law, the life of the brain must be just as much subject to it as the reversible processes that are not dependent on time.” Thus, Hering says in his lecture on “Memory” already alluded to: “(The facts of mind, consciousness, and so forth) cannot make the human body to be anything else but that which it is--a complex of matter subject to laws not to be turned aside by anything,--laws followed by the material of the stone, by the substance of the plant.” With this, however, the biologist is put in a difficult position. He is all unaware that the reversible processes are “subject” to the law of the conservation of energy, _i.e._ may be read by it, only because it is possible here to be satisfied with reactions, only because here one does not need to know anything about the energies themselves, because here there is no “_I_”-sayer who might raise objections to such a mode of apprehending things. The greatness, the exactitude of physics consist precisely in this, that she confines herself strictly to the realm of reactions. In the life of the brain, so far as directly manifested--as consciousness--there are no reactions. The fact “consciousness” in others is not accessible to me; and as for myself, here action and reaction always merge into one another, though I go to work with never so elaborate psycho-physiological precautions. Hence the necessity of ever and again laying out fresh frontier domains, such as bio-chemistry, bio-kinetics, and so forth and so on, so as to be able to say with Lady Macbeth, “We are yet young in deeds!” Thus, patience! Let us but once get these new courses drawn up and then--how the results will come flowing in! But the only new thing about these courses is the name! In truth, here as everywhere, we have to do with the old, original problem “life”--at once our hope and our despair. And to all these new courses, by means of which men hope to master the old problem, applies that answer of Pompey’s favourite cook when his master marvelled at the host of different dishes, “All one meat: only the sauces are different.” For it is even the same here, “All one thing: only the names are different.”