on every gesture, and so do genius and a reflective nature. Hence the

outcome of La Bruyere's remark: _Il n'y a rien de si délié, de si simple, et de si imperceptible où il n'y entrent des manières, qui nous décèlent: un sot ni n'entre, ni ne sort, ni ne s'assied, ni ne se lève, ni ne se tait, ni n'est sur ses jambes, comme un homme d'esprit_. This accounts for, by the way, that instinct _stir et prompt_ which, according to Helvetius, ordinary people have of recognising people of genius and of running away from them. This is to be accounted for by the fact that the larger and more developed the brain, and the thinner, in relation to it, the spine and nerves, the greater not only is the intelligence, but also at the same time the mobility and pliancy of all the limbs; because they are controlled more immediately and decisively by the brain; consequently everything depends more on a single thread, every movement of which precisely expresses its purpose. The whole matter is analogous to, nay dependent on, the fact that the higher an animal stands in the scale of development, the easier can it be killed by wounding it in a single place. Take, for instance, batrachia: they are as heavy, clumsy, and slow in their movements as they are unintelligent, and at the same time extremely tenacious of life. This is explained by the fact that with a little brain they have a very thick spine and nerves. But gait and movement of the arms are for the most part functions of the brain; because the limbs receive their motion, and even the slightest modification of it, from the brain through the medium of the spinal nerves; and this is precisely why voluntary movements tire us. This feeling of fatigue, like that of pain, has its seat in the brain, and not as we suppose in the limbs, hence motion promotes sleep;