Split the lark and you'll find the music

Split the lark and you'll find the music,
Bulb after bulb, in silver rolled,
Scantily dealt to the summer morning,
Saved for your ear when lutes be old.

Loose the flood, you shall find it patent,
Gush after gush, reserved for you;
Scarlet experiment! sceptic Thomas,
Now, do you doubt that your bird was true?