The facts of localization of function, however, do not agree so well with this tool conception of the brain, which always leads us back again to the theory that the mind takes hold of its tool at a single point. If the mind can suffer or produce _this_ change only here, _that_ change only there, it is difficult to see why we should regard it as an altogether separate entity. Some have pointed out, as an analogy, that truth too is everywhere, and because of its absolute unity, everywhere in its totality, without being bound to space and time. I must doubt, however, if truth is present where such analogies are worked out, for nothing can be less clear than the assertion that truth has unity. Mind is not everywhere in its totality, neither in the brain nor in the whole world. It is partly here, partly there; as seeing mind it is in the occipital convolutions of the brain, as hearing mind in the temporal convolutions. Thus we are forced, if we regard the brain as the mind’s tool, to regard the mind as an entity possessing spatial form. If we reject this conclusion, we must also reject the premise that the brain is the mind’s tool. There are two other difficulties of very considerable importance. One of them is compliance with the principle of the conservation of energy. If mind is an entity independent of the brain, if the brain is a tool which mind can use arbitrarily, without having to obey the laws of the material world, there would be a serious break in the continuity of natural law, and the principle of the conservation of energy would suffer an exception. Until recently it was, not probable, but at least possible, that this principle of the conservation of energy was not strictly correct when applied to conscious beings, especially to man. But in recent years direct experiment has proved that it applies to the dog, and even to man. In an animal performing no gross muscular work the energy supplied by the food is completely transformed into heat, which is absorbed by the animal’s surroundings. Rubner has found as the result of very exact measurements that the heat produced by an animal during several weeks is within one half of one per cent (that is, within the probable error) equal to the quantity of chemical energy received from the food. One might think that it would be rash to apply conclusions reached by experimenting on a dog to man, whose mental life stands on a much higher level. But even this objection has been removed by Atwater. He performed similar experiments on five educated persons, varying the conditions of mental and muscular activity or relative rest. The result is the same. Taking the total result, there is absolute equality between the energy supplied and the energy given out; in the human organism, mind has thus been proved to be subject to the laws of the natural world.