The secret is, that, though the country offers to farmers more oxygen than to anybody in the city, yet not all dwellers in the country are farmers, and even those who are such are suffering from other causes, being usually the very last to receive those lessons of food and clothing and bathing and ventilation which have their origin in cities. Physical training is not a mechanical, but a vital process: no bricks without straw; no good _physique_ without good materials and conditions. The farmer knows, that, to rear a premium colt or calf, he must oversee every morsel that it eats, every motion it makes, every breath it draws,--must guard against over-work and under-work, cold and heat, wet and dry. He remembers it for the quadrupeds, but he forgets it for his children, his wife, and himself: so his cattle deserve a premium, and his family does not. Neglect is the danger of the country; the peril of the city is in living too fast. All mental excitement acts as a stimulant, and, like all stimulants, debilitates when taken in excess. This explains the unnatural strength and agility of the insane, always followed by prostration; and even moderate cerebral excitement produces similar results, so far as it goes. Quetelet discovered that sometimes after lecturing, or other special intellectual action, he could perform gymnastic feats impossible to him at other times. The fact is unquestionable; and it is also certain that an extreme in this direction has precisely the contrary effect, and is fatal to the physical condition. One may spring up from a task of moderate mental labor with a sense of freedom like a bow let loose; but after an immoderate task one feels like the same bow too long bent, flaccid, nerveless, all the elasticity gone. Such fatigue is far more overwhelming than any mere physical exhaustion. I have lounged into the gymnasium, after an afternoon's skating, supposing myself quite tired, and have found myself in excellent condition; and I have gone in after an hour or two of some specially concentrated anxiety or thought, without being aware that the body was at all fatigued, and found it good for nothing. Such experiences are invaluable; all the libraries cannot so illustrate the supremacy of immaterial forces. Thought, passion, purpose, expectation, absorbed attention even, all feed upon the body's powers; let them act one atom too intensely or one moment too long, and this wondrous physical organization finds itself drained of its forces to support them. It does not seem strange that strong men should have died by a single ecstasy of emotion too convulsive, when we bear within us this tremendous engine whose slightest pulsation so throbs in every fibre of our frame.