This necessitates on the part of all young animals incessant changes of action, or alternations of action and repose.

A farmer of forty years of age, whose organs are well developed and mature, will chop wood all day without excessive fatigue.

Then, when he comes home at night, he will sit for three hours in the evening upon the settle by his fireside, _thinking_--his mind occupied, perhaps, upon the details of the management of his farm, or upon his plans for the following day.

The vital force thus expends itself for many successive hours through his muscles, and then, while his muscles are at rest, it finds its egress for several other hours through the brain.

But in the _child_ the mode of action must change every few minutes.