How many breaths do these lungs have left?

How many breaths do these lungs have left?
How many beats will this heart beat till it’s end?
How many licks will it take to get to the center of this tootsie pop?
The world will soon know.
If not today, tomorrow my soul will have lept,
Soon I will go ‘round the bend,
The green ichor life will depart, without a drop.
Never again to grow.
The third brother I am, he who death had not met,
Only when ready, the cloak to his son he did send.
Ready for his story to stop.
Ready to open at the close.
Yet the choice is not mine, when to be cleft,
But up to the scythe, the instrument to unmend,
It is me he will lop
Until the next one is sewn.