The human body is a furnace which keeps in blast three-score years and ten, more or less.

It burns about three hundred pounds of carbon a year, (besides other fuel,) when in fair working order, according to a great chemist's estimate.

When the fire slackens, life declines; when it goes out, we are dead.
It has been shown by some noted French experimenters, that the amount of combustion increases up to about the thirtieth year, remains stationary to about forty-five, and then diminishes.

This last is the point where old age starts from.

The great fact of physical life is the perpetual commerce with the elements, and the fire is the measure of it.
About this time of life, if food is plenty where you live,--for that, you know, regulates matrimony,--you may be expecting to find yourself a grandfather some fine morning; a kind of domestic felicity that gives one a cool shiver of delight to think of, as among the not remotely possible events.
I don't mind much those slipshod lines Dr.Johnson wrote to Thrale, telling her about life's declining from THIRTY-FIVE; the furnace is in full blast for ten years longer, as I have said.