Even a superficial glance is sufficient to show that all the innumerable forms in which the life-urge of Nature manifests itself are subject to a fundamental law - one may call it an iron law of Nature - which compels the various species to keep within the definite limits of their own life-forms when propagating and multiplying their kind.
A sense is what has the power of receiving into itself the sensible forms of things without the matter, in the way in which a piece of wax takes on the impress of a signet-ring without the iron or gold.
My child, what I want is muscles of iron and nerves of steel, inside which dwells a mind of the same material as that of which the thunderbolt is made.
Life is not as idle ore,
But iron dug from central gloom,
And heated hot with burning fears,
And dipt in baths of hissing tears,
And batter'd with the shocks of doom,
To shape and use.
As great Pythagoras of yore,
Standing beside the blacksmith's door,
And hearing the hammers, as they smote
The anvils with a different note,
Stole from the varying tones, that hung
Vibrant on every iron tongue,
The secret of the sounding wire.
And formed the seven-chorded lyre.