The Mind's Diet

No life worth naming ever comes to good
If always nourished on the selfsame food;
The creeping mite may live so if he please,
And feed on Stilton till he turns to cheese,
But cool Magendie proves beyond a doubt,
If mammals try it, that their eyes drop out.

No reasoning natures find it safe to feed,
For their sole diet, on a single creed;
It spoils their eyeballs while it spares their tongues,
And starves the heart to feed the noisy lungs.

When the first larvae on the elm are seen,
The crawling wretches, like its leaves, are green;
Ere chill October shakes the latest down,
They, like the foliage, change their tint to brown;
On the blue flower a bluer flower you spy,
You stretch to pluck it - 'tis a butterfly;
The flattened tree-toads so resemble bark,
They're hard to find as Ethiops in the dark;
The woodcock, stiffening to fictitious mud,
Cheats the young sportsman thirsting for his blood;
So by long living on a single lie,
Nay, on one truth, will creatures get its dye;
Red, yellow, green, they take their subject's hue, -
Except when squabbling turns them black and blue!