“ The great fact of physical life is the perpetual commerce with the elements, and the fire is the measure of it. ”
 Oliver Wendell Holmes Sr., The Autocrat of the Breakfast-Table (1858). copy citation

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“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.” source